powerpc's asm/prom.h brings some headers that it doesn't
need itself.

In order to clean it up, first add missing headers in
users of asm/prom.h
Signed-off-by: NChristophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/f98acba303489bdf003e7256460696225b00702e.1648833428.git.christophe.leroy@csgroup.euSigned-off-by: NVinod Koul <vkoul@kernel.org>