minigbm: mediatek: add support HAL_PIXEL_FORMAT_YV12

minigbm: mediatek: add support HAL_PIXEL_FORMAT_YV12

For some reason, we use HAL_PIXEL_FORMAT_YV12 instead of
HAL_PIXEL_FORMAT_YCbCr_420_888 as our YUV format on mediatek
based boards. We also pass down a different use flags. Since
mediatek only supports linear buffers the moment, just lump all
the flags together for our YUV supported combination.

BUG=chromium:616275
TEST=Played Youtube video in Oak ARC++ container
CQ-DEPEND=CL:416292

Change-Id: Iac4797517048981235cd17ad464eb1e3852c4072
Reviewed-on: https://chromium-review.googlesource.com/416396
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>