vts: Use HAL_PIXEL_FORMAT_YCBCR_420_888 for the encoder input buffer

Supporting HAL_PIXEL_FORMAT_YCBCR_420_888 format is the codec2
encoder requirement, while supporting HAL_PIXEL_FORMAT_YV12 is
optional. HAL_PIXEL_FORMAT_YCBCR_420_888 should be used for the
encoder input format in VTS.

Bug: 395974992
Test: VtsHalMediaC2V1_0TargetVideoEncTest
Flag: EXEMPT test
Change-Id: If167bf1fc0da594c0ff3153d75ed8ccf595f00b3