Translate AHARDWAREBUFFER_FORMAT_Y8Cb8Cr8_420 to NV12
... as this is what Minigbm Gralloc uses as the underlying format
for the flexible YCbCr 420 format.
Bug: b/234047309
Test: `launch_cvd --gpu_mode=gfxstream` with ANGLE on Gfxsteam VK
and open camera app
Change-Id: If20aaad83d4076ac04301f7391fe809743850a11