drm/atmel-hlcdc: Use per-plane rotation property

The global mode_config.rotation_property is going away, switch over to
per-plane rotation_property.

v2: Propagate error upwards (Boris)
v3: Drop the BIT()

Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1474907460-10717-6-git-send-email-ville.syrjala@linux.intel.com