gralloc4: Update YV12 alignment to conform to platform contract

After this patch, GPU usages are not guaranteed to conform to platform's
contract, but others will be.

Bug: 274375412
Test: gfx-gralloc-alloc-test
Test: Manually tested GPU rendering using map-graphics-buffer tool
Change-Id: I3a0202c61d3e558595a856ec150d12be5a7220fc