iommu: msm: move L2 redirect to a domain attribute

We will soon be removing the `flags' parameter from iommu_domain_alloc
and iommu_ops.domain_init. In preparation for this, move the L2 redirect
flag to a domain attribute.

We now no longer need the extra parameter to iommu_domain_alloc which
was added in [8984b0e3: "drivers: iommu: Add flags to
iommu_domain_alloc"] since we're changing the way L2 redirect is
configured. Remove it.

Change-Id: Ie0d15767ca08211740d22568683fae01e8123a26
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>