msm: kgsl: Allow I/O coherency on imported buffers if we can

Allow I/O coherency to be enabled on imported buffers if I/O coherency
is enabled and we can determine the cache characteristics of the
imported buffer. The caller should check the flags after allocation
to determine if I/O coherency was enabled.

Change-Id: Ic0dedbade77189bd51dddad64d15f0835601e925
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>