drm: add plane properties

The omapdrm driver uses this for setting per-overlay rotation.  It
is likely also useful for setting YUV->RGB colorspace conversion
matrix, etc.

Signed-off-by: Rob Clark <rob@ti.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>