iommu: Remove support for buffer alignment to ARM_SMMU_MIN_IOVA_ALIGN

Remove the support to align the start and end of all mapped
buffers to ARM_SMMU_MIN_IOVA_ALIGN as the support is
no longer required.

Change-Id: I285411124eea3d4836db1537a2b51066a27c5f24
Signed-off-by: Swathi Sridhar <swatsrid@codeaurora.org>