drm: mali-dp: Add support for setting plane's rotation property from userspace.

In order to support DRM_IOCTL_MODE_OBJ_SETPROPERTY for the rotation property
we need to have a ->set_property hook defined for the planes. Set the
plane's ->set_property hook to drm_atomic_helper_plane_set_property()

Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>