minigbm: gralloc0: Allow lock_ycbcr for HAL_PIXEL_FORMAT_IMPLEMENTATION_DEFINED

minigbm: gralloc0: Allow lock_ycbcr for HAL_PIXEL_FORMAT_IMPLEMENTATION_DEFINED

We can use lock_ycbcr as a way to partially work around the format resolve
problem - with the assumption that if lock_ycbcr succeeds, the
android_ycbcr struct returned describes a YCbCr 4:2:0 image, we can
query gralloc for the format instead of hardcoding one statically.

BUG=b:32077885
TEST=Camera preview renders correctly on Poppy.

Change-Id: Ic20f5aa89809bf89941f3b4851c0d28965da54ac
Reviewed-on: https://chromium-review.googlesource.com/544487
Commit-Ready: Tomasz Figa <tfiga@chromium.org>
Tested-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>