drivers: iommu: Add flags to iommu_domain_alloc

Add the ability to pass flags into the iommu_domain_alloc
function to specify domain attributes.

Change-Id: Ia33aa8d887a57f76d97ab8921385dcc551716846
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>
[sboyd: Only iommu_domains.c part]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>