accel/rocket: Depend on DRM_ACCEL not just DRM

accel/rocket: Depend on DRM_ACCEL not just DRM

With the current dependency on only DRM, a config of

CONFIG_DRM_ACCEL_ROCKET=y

is possible, but of course wrong, because without DRM_ACCEL the build-
system will never even enter drivers/accel/* .

So depend on DRM_ACCEL instead of just DRM.

Fixes: ed98261b4168 ("accel/rocket: Add a new driver for Rockchip's NPU")
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Tomeu Vizoso <tomeu@tomeuvizoso.net>
Link: https://lore.kernel.org/r/20250814113519.1551855-3-heiko@sntech.de