arm64: dts: imx8mp: Add LCDIF2 & LDB nodes

LCDIF2 is directly attached to the LVDS Display Bridge (LDB).
Both need the same clock source (VIDEO_PLL1).

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Tested-by: Richard Leitner <richard.leitner@linux.dev>
Tested-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>