linux-firmware: add new package for Mali CSFFW Valhall firmware

This firmware is necessary for closed-source mali blob + drivers and
open-source Panthor (via Mesa + Linux kernel) drivers.

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>