iommu/arm-smmu: add support for TTBR0, CONTEXTIDR and PROCID attributes

Add fields to arm_smmu_cfg to store asid, vmid, and procid so that they
can queried easily.

Program the CONTEXTIDR register during attach so that the PROCID
attribute functions as expected.

Change-Id: I2e2b3926fbf021754e89edda9a6857d2e3a7138b
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>