minigbm: Ensure DRM_FORMAT_YVU420_ANDROID meets Android requirements.

minigbm: Ensure DRM_FORMAT_YVU420_ANDROID meets Android requirements.

For HAL_PIXEL_FORMAT_YV12 (mapped to DRM_FORMAT_YVU420_ANDROID), it
needs to meet the following requirements:
 - The vertical stride must equal to the buffer's height.
 - The chroma stride is 16-byte aligned.

As a result, stop mapping DRM_FORMAT_FLEX_YCbCr_420_888 to
DRM_FORMAT_YVU420_ANDROID. The format is used for hardware decoding,
It has more restrictions on the alignments of the width or height.

Bug: b:31479749
Test: Run the testOtherVP8ImageReader and testGoogH264ImageReader of
      android.media.cts.ImageReaderDecoderTest.

Change-Id: Id37f51115ed8b1937ca7d6e48abd809235b43fe4
Reviewed-on: https://chromium-review.googlesource.com/526758
Commit-Ready: Owen Lin <owenlin@chromium.org>
Tested-by: Owen Lin <owenlin@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>