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/5ed3298d8b5b1b5bf681d79584c61cb495852f4e.1648833423.git.christophe.leroy@csgroup.euSigned-off-by: NMark Brown <broonie@kernel.org>