This enables CDEF for chroma when the horizontal and vertical
subsampling differs.  Since the direction search is only performed in
luma, the following corrections to the direction index are done for
chroma to correct the distortion resulting from the subsampling:

4:2:2:   4:4:0:
0 -> 7   0 -> 1
1 -> 0   1 -> 2
2 -> 2   2 -> 2
3 -> 4   3 -> 2
4 -> 5   4 -> 3
5 -> 6   5 -> 4
6 -> 6   6 -> 6
7 -> 6   7 -> 0

This improves the chroma PSNR BDR by about 2% for 4:2:2 content at
cpu-used=4, low delay configuration.  4:2:0 and 4:4:4 content is
unchanged.

Change-Id: Iee92d3697bc5a6fc9b1f340a63243a334935b433