iommu: msm: add support for DOMAIN_ATTR_CONTEXT_BANK

Add support for DOMAIN_ATTR_CONTEXT_BANK to query the
context bank ID from the msm iommu legacy driver.

Change-Id: I60cc4442803f49051f9d414fed6e6df4e10f08de
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>