msm: vidc: Add support for decoder downscaling

Venus FW supports downscaling for decoder. Venus
FW sends the supported downscaled ratios. Driver
needs to make sure that the scaling is inside the
supported range. This change adds the support for
decoder downscaling.

Change-Id: I919e563a6ba64751b3355658bcdbcec9d9ef17eb
Signed-off-by: Praneeth Paladugu <ppaladug@codeaurora.org>