For the cbcr format, gt2 and gt4 are computed again after src_h has been divided by vsub.
As src_h as already been divided by 2 before, introduce cbcr_src_h and cbcr_src_w to keep a copy of those values to be used for cbcr gt2 and gt4 computation.
This fixes yuv planes being unaligned vertically when down scaling to 1080 pixels from 2160.