linux-firmware: package amdgpu firmware

Add packages for the firmware required by amdgpu kernel driver.

Signed-off-by: Vincent Davis Jr <vince@underview.tech>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
(cherry picked from commit 0d7aa21f)
Signed-off-by: Steve Sakoman <steve@sakoman.com>