imx-drm: use supplied drm_device where possible

The component helper provides us the drm_device which is being
registered.  Rather than having to reference a global in imx-drm-core,
use this to get the imxdrm device, and also use it to register the CRTC
against.

This means we never have CRTCs/encoders/connectors without the drivers
private data being accessible.

Remove the module owner field as well; this provides no protection
against the device being unbound.

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>