drm/amd/display: Use two pixel per container for k1/k2 div

Currently, we check if pixel_encoding is equal to
PIXEL_ENCODING_YCBCR422 to get the k1/k2 div parameters. This commit
changes this logic slightly by checking if two pixels per container are
used.

Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>