Add the following properties for planes:
* alpha
* pixel blend mode. Only "Pre-multiplied" and "Coverage" are supported
Signed-off-by: NJean-Jacques Hiblot <jjhiblot@ti.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190711135219.23402-1-jjhiblot@ti.com