The UV plane is the master plane that does all color correction etc.
It needs to be programmed with the dimensions for color plane 1 (UV).

The Y plane just feeds the Y pixels to it. Program the scaler from the
master only, and set PLANE_CTL_YUV420_Y_PLANE on the slave plane.

Changes since v1:
- Make a common skl_program_plane, and use it for both plane updates.
Changes since v2:
- Make color_plane explicit, to clarify skl_update_plane(). (Ville)
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181018115134.9061-8-maarten.lankhorst@linux.intel.com