iommu/fsl_pamu: Prepare cleanup of powerpc's asm/prom.h

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: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/06862cca930068e8fa4fdd0b20d74872d3b929d6.1648833431.git.christophe.leroy@csgroup.eu
Signed-off-by: Joerg Roedel <jroedel@suse.de>