imx-drm: imx-drm-core: skip components whose parent device is disabled

In a board setup which disables LDB device node completely by changing
status to 'disabled', and only enables HDMI device, we're running into
the problem that imx-drm master never succeeds in binding, and hence
HDMI does not come up either.

&ldb {
	status = "disabled";

	lvds-channel@1 {
		...
		status = "okay";
	};
};

The imx-drm-core should really skip the LVDS channels no matter what
lvds-channel's status is, if LDB device is disabled.  Let's consider
such setup a misconfiguration, give a warning in there and not add the
component.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>