imx-drm: imx-drm-core: provide helper function to parse possible crtcs
Provide a helper function to parse possible crtcs before the encoder
is registered. The crtc mask is derived from the position of the
CRTCs registered in the drm_device.
Acked-by: Philipp Zabel <p.zabel@pengutronix.de> Acked-by: Shawn Guo <shawn.guo@linaro.org> Reviewed-by: Fabio Estevam <fabio.estevam@freescale.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>