drm/amd/display: Fix two MPO videos in single display ODM combine mode

[Why]
In single display ODM combine mode, two MPO videos ( three
 planes ) are not working

[How]
When we detect three planes, don't set odm combine 2to1 policy
 for the MPO planes.  Otherwise, we run out of pipes available
Add support for two MPO videos in dc_add_plane_to_context().
 Don't allow both videos to be on the same side of the
 display.
Add extra check when fetching free pipe for two MPO videos.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Samson Tam <Samson.Tam@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>