drm/amd/display: Fix LB BPP and Cursor width

DCN2.0 LB BPP should be 48 or 16BPC and max cursor width should be 256.

Also use populate_dml_pipes as functions pointer instead of using it directly

Signed-off-by: Ilya Bakoulin <Ilya.Bakoulin@amd.com>
Reviewed-by: Eric Bernstein <Eric.Bernstein@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>