drm/i915: Remove special case slave handling during hw programming, v3.

Now that we split plane_state which I didn't want to do yet, we can
program the slave plane without requiring the master plane.

This is useful for programming bigjoiner slave planes as well. We
will no longer need the master's plane_state.

Changes since v1:
- set src/dst rectangles after copy_uapi_to_hw_state.
Changes since v2:
- Use the correct color_plane for pre-gen11 by using planar_linked_plane != NULL.
- Use drm_format_info_is_yuv_semiplanar in skl_plane_check() to fix gen11+.

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/20191031112610.27608-12-maarten.lankhorst@linux.intel.com