iommu/arm-smmu: Remove depends on ARCH

Each qcom ARCH platform should select MSM_TZ_SMMU by
needed via select in Kconfig or use defconfig, while
driver itself is ARCH independent, so remove depends
on ARCH from MSM_TZ_SMMU Kconfig.

Change-Id: I877a15b74032236ac71b84e672e135a20589ba36
Signed-off-by: Maria Yu <aiquny@codeaurora.org>