video: tegra: nvmap: treat writecombine requests as dmacoherent

video: tegra: nvmap: treat writecombine requests as dmacoherent

NvMap always allocates DRAM or IRAM memory. It never allocates real
Device memory. From Arm v8 onwards writecombine memory is real
writecombine, which is of less performace for DRAM accesses and
unnecessary for DRAM.
Treat writecombine requests as dmacoherent, which is normal memory
non-cacheable.

Change-Id: I5c19a5f0f033eec3680bf6b9db1cbbfb02090f3d
Signed-off-by: Krishna Reddy <vdumpa@nvidia.com>
Reviewed-on: http://git-master/r/379702
GVS: Gerrit_Virtual_Submit
Reviewed-by: Sri Krishna Chowdary <schowdary@nvidia.com>