msm: kgsl: Do not mark all buffers as iocoherent

Add a check to mark only cached buffers as iocoherent.
We can't enable io-coherency for uncached buffers because
of situations where hardware might snoop the cpu caches
which can have stale data.This happens primarily due to the
limitations of dma caching APIs available on arm64.

Change-Id: Iafad086d38559139cb45f6a290071ec6d58ad3a3
Signed-off-by: Urvashi Agrawal <urvaagra@codeaurora.org>