drm: xlnx: zynqmp_dpsub: Add global alpha support

The graphics plane has a global alpha setting. Expose it through the
plane's alpha property.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
This commit is contained in:
Laurent Pinchart 2021-03-07 02:56:58 +02:00
commit 650f12042b