Now that we implemented support for planar formats on gen11, we can
finally advertise it.

Changes since v1:
- Re-add change to skl_plane_has_planar(), was lost in rebase noise.
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181022134514.14756-1-maarten.lankhorst@linux.intel.com