imx-drm: imx-drm-core: get rid of drm_mode_group_init_legacy_group()

imx-drm: imx-drm-core: get rid of drm_mode_group_init_legacy_group()

Since we're now operating like a conventional DRM driver, doing all
the initialisation within the driver's ->load callback, we don't
need to mess around with the mode groups - we can rely on the one
in the DRM platform code.

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>