ARM: dts: renesas: r8a7740: Add LCDC nodes

Add device nodes for the two LCD Controllers (LCDC) on the R-Mobile A1
SoC, and for the two optional external LCDL clock inputs.

Note that the HDMI clock for LCDC1 is not added, as this clock is not
yet supported.

Based on a patch by Laurent Pinchart adding the first LCDC device node.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/12dcec10e6fb3b55c39f6221349d35d6d6f17a5d.1700669207.git.geert+renesas@glider.be