Remove the LDB endpoint description from the common imx6sx.dtsi
as it causes regression for boards that has the LCDIF connected
directly to a parallel display.

Let the LDB endpoint be described in the board devicetree file
instead.

Cc: stable@vger.kernel.org
Fixes: b74edf62 ("ARM: dts: imx6sx: Add LDB support")
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>