drivers/base/iommu.c: add missing includes

Fix zillions of -mm x86_64 allmodconfig build errors - the file uses
EXPORT_SYMBOL() and kmalloc but misses the needed includes.

Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>