PCI: hotplug: Clean up include files

arch/powerpc/include/asm/prom.h includes some headers that it doesn't need
itself.  Add the missing headers to files that include prom.h so we can
remove them from prom.h.

Link: https://lore.kernel.org/r/79201f5fae8d003164ac36ed3be7789db1bc5ab4.1648833421.git.christophe.leroy@csgroup.eu


Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>