msm: allow allocation of NV12 dumb buffers

msm: allow allocation of NV12 dumb buffers

Cheza's codec validation requires the ability to import external buffers
into the codec driver. However the only possible provider of such
buffers so far is the display. Make it possible to allocate dumb NV12
buffers by adding the format to the list of allowed formats, and
adjusting the requested buffers' height to include room for the UV plane
and extra padding the venus driver requires.

BUG=b:80589901
TEST=Checked that VDA unittest's TestDecodeTimeMedian passed in import
mode on Cheza.

Change-Id: I6993f654a3bf5e64cdf8a1c665c60bb4c7d9cc9a
Reviewed-on: https://chromium-review.googlesource.com/1118078
Commit-Ready: Alexandre Courbot <acourbot@chromium.org>
Tested-by: Alexandre Courbot <acourbot@chromium.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>