iommu/renesas: Expand COMPILE_TEST coverage

This driver shouldn't need anything architecture-specific (that isn't
under CONFIG_ARM protection already), and has already been accessible
from certain x86 configurations by virtue of the previously-cleaned-up
"ARM || IOMMU_DMA" dependency. Allow COMPILE_TEST for all architectures.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/1fe2006aa98f008a2e689adba6e8c96e9197f903.1593791968.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>