bes2600: drop BES2600_WRITE_DPD_TO_FILE kernel_*() file paths

bes_chardev.c carried three functions gated behind the
BES2600_WRITE_DPD_TO_FILE Kconfig/make-flag (default off):

  - bes2600_chrdev_write_dpd_data_to_file()
      filp_open(O_CREAT | O_TRUNC | O_RDWR) + kernel_write()
      writing a raw DPD calibration blob back to
      BES2600_DPD_PATH (default /data/cfg/bes2600_dpd.bin, an
      Android-AOSP path).

  - bes2600_chrdev_read_and_check_dpd_data()
      filp_open(O_RDONLY) + kernel_read() reading the DPD blob
      from either BES2600_DPD_GOLDEN_PATH (/data/cfg/…) or
      BES2600_DEFAULT_DPD_PATH (/lib/firmware/bes2600_dpd.bin),
      followed by a CRC/version sanity check.

  - bes2600_chrdev_dpd_is_vaild() (sic), the CRC/version helper
    used only by the read path.

Plus the bes_cdev.no_dpd field, its module_param, and two
intrusion sites in bes2600_chrdev_get_dpd_data() and
bes2600_chrdev_update_dpd_data() that invoke the above.

The Makefile defaults BES2600_WRITE_DPD_TO_FILE=n, so in a stock
build all of this is dead code. It is still a standing upstream
blocker for exactly the same reasons as the factory-txt write
path removed in the preceding patch:

  - filp_open() + kernel_read()/kernel_write() bypass the
    firmware-class abstraction and LSM-governed access control
    that apply to /lib/firmware/.
  - The write target /data/cfg/ is an Android AOSP convention
    that does not exist on a Linux distribution and cannot be
    created by the kernel anyway.
  - A runtime DPD re-calibration is intended to reduce TX EVM
    after temperature or aging drift; persisting the result via
    kernel_write() is fundamentally a userspace concern (debugfs
    dump + userspace tool is the expected route).

Remove the entire #ifdef BES2600_WRITE_DPD_TO_FILE block from
bes_chardev.c (including the inner #ifdef inside
bes2600_chrdev_read_and_check_dpd_data() guarding a
DPD_BIN_FILE_SIZE size check that only applied to the read-back-
its-own-write case), the no_dpd field and module_param, and the
two invocation sites. Drop the Kconfig/make-flag and the three
associated PATH macros from the Makefile. Net: -155 lines, no
remaining filp_open/kernel_read/kernel_write anywhere in
bes_chardev.c.

The in-memory DPD state path is unchanged: bes2600_chrdev_get_dpd_
buffer() still allocates a kmalloc'd buffer used by the firmware-
download path, bes2600_chrdev_update_dpd_data() still validates
the buffer's CRC and transitions bes2600_cdev.wait_state on
success, and bes2600_chrdev_free_dpd_data() still releases the
buffer on unload. Only the file-I/O side-channel is removed.

Signed-off-by: Markus Fritsche <fritsche.markus@gmail.com>

bes2600/Makefile

@@ -28,7 +28,6 @@ CONFIG_BES2600_WIFI_BOOT_ON             ?= y
 CONFIG_BES2600_BT_BOOT_ON               ?= n
 
 BES2600_GPIO_WAKEUP_AP                  ?= n
-BES2600_WRITE_DPD_TO_FILE               ?= n
 BES2600_TX_MORE_RETRY                   ?= n
 
 # bes evb
@@ -93,12 +92,6 @@ ccflags-y += -DBES_UNIFIED_PM
 ccflags-y += -DBES_SDIO_OPTIMIZED_LEN
 ccflags-y += -DBES2600_HOST_TIMESTAMP_DEBUG
 
-ifeq ($(BES2600_WRITE_DPD_TO_FILE),y)
-BES2600_DPD_PATH ?= /data/cfg/bes2600_dpd.bin
-BES2600_DEFAULT_DPD_PATH ?= /lib/firmware/bes2600_dpd.bin
-BES2600_DPD_GOLDEN_PATH ?= /data/cfg/bes2600_dpd_golden.bin
-endif
-
 ifeq ($(BES2600_DUMP_FW_DPD_LOG),y)
 BES2600_DPD_LOG_PATH ?= /data/applog/bes2600_dpd_log.log
 endif
@@ -135,9 +128,6 @@ ccflags-y += $(call boolen_flag,BSS_LOSS_CHECK,y)
 ccflags-y += $(call string_flag,BES2600_LOAD_FW_TOOL_PATH)
 ccflags-y += $(call string_flag,BES2600_LOAD_FW_TOOL_DEVICE)
 ccflags-y += $(call string_flag,BES2600_DRV_VERSION)
-ccflags-y += $(call string_flag,BES2600_DPD_PATH)
-ccflags-y += $(call string_flag,BES2600_DEFAULT_DPD_PATH)
-ccflags-y += $(call string_flag,BES2600_DPD_GOLDEN_PATH)
 
 ccflags-y += $(call boolen_flag,BES2600_INDEPENDENT_EVB,y)
 ccflags-y += $(call boolen_flag,BES2600_INTEGRATED_MODULE_V1,y)
@@ -159,8 +149,6 @@ ccflags-y += $(call boolen_flag,FACTORY_SAVE_MULTI_PATH,y)
 ccflags-y += $(call boolen_flag,FACTORY_CRC_CHECK,y)
 
 ccflags-y += $(call boolen_flag,BES2600_GPIO_WAKEUP_AP,y)
-ccflags-y += $(call boolen_flag,BES2600_WRITE_DPD_TO_FILE,y)
-
 ccflags-y += $(call boolen_flag,BES2600_DUMP_FW_DPD_LOG,y)
 ccflags-y += $(call string_flag,BES2600_DPD_LOG_PATH)