linux-ampere-fourier: bump to kafr2 (v7.0-rc3 + fleet/ampere.yaml manifest)

Drops the f8f3ad9 baseline ("18 commits ahead, BLACK-SCREENS ampere"
per fleet/ampere.yaml bisect note) in favor of the kernel-agent-
managed 10-patch set produced by ka-promote from fleet/ampere.yaml.

Baseline: mainline v7.0-rc3 (3daa4f5dc6cc), plus the 10 scope-tagged
patches under marfrit/kernel-agent/patches/{soc,module,board,driver}/:
  - 1 soc/rk3588 pwm15 pinctrl
  - 6 board/coolpi-cm5-genbook DTS patches
  - 3 driver/media Sarma VP9-on-VDPU381 patches (PR #24 closure)

New _commit 48a8c78 reflects this tree state in ~/src/linux-rockchip
(branch vp9-build on ampere, exactly v7.0-rc3 + 10 manifest patches).

End-to-end verified before this iteration was cut (hand-build of the
same tip on 2026-05-18 booted ampere via arch_vp9_test extlinux
label):
  - VP9 decode bit-exact HW==SW==libva (sha c8624d7c42db66525f53a02a515bc38d0a17ef39f692660cc7bebb1e2d2e1b48)
  - AV1 decode bit-exact HW==SW via kdirect (sha 30d2091158d92f3c5e0a807217c3e7307f873267673d92632e7fb147383e7dd1, av1-vpu-dec is mainline 7.0)

prebuild.sh canonical sha256 cleared — gzip-version-dependent, the
script warns-not-fails on mismatch. First successful kafr2 build can
pin a canonical sha here if a reproducibility audit ever needs it.

Cross-references:
  - marfrit/kernel-agent#12 (VP9 enablement closure)
  - marfrit/kernel-agent PR #24 (Sarma patch import + ampere.yaml bump)

arch/linux-ampere-fourier/prebuild.sh

@@ -19,8 +19,11 @@
 set -euo pipefail
 
 TREE="${LINUX_RK3588_MARFRIT_TREE:-${HOME}/src/linux-rockchip}"
-COMMIT=f8f3ad934433bd7e1207d9b0b37e817a692b7ee9
-SHA256_EXPECTED=b4eca11e883fe6f7f306d8751c3efa3afed9cc3465c74a3320de1b7204f5f330
+COMMIT=48a8c785de7f5320513052a64e544c6310d7b273
+# Generated tarball sha varies with gzip version — script warns-not-fails.
+# Leave EXPECTED empty for fresh kafr2 builds; first successful build can
+# pin a canonical sha here if a reproducibility audit needs it.
+SHA256_EXPECTED=
 
 HERE="$(cd "$(dirname "$0")" && pwd)"
 OUTPUT="${HERE}/linux-rk3588-marfrit-${COMMIT:0:7}.tar.gz"