dt-bindings: display: Document Renesas RZ/G2L DU bindings

The RZ/G2L LCD controller is composed of Frame Compression Processor
(FCPVD), Video Signal Processor (VSPD), and Display Unit (DU).

The DU module supports the following hardware features
− Display Parallel Interface (DPI) and MIPI LINK Video Interface
− Display timing master
− Generates video timings
− Selecting the polarity of output DCLK, HSYNC, VSYNC, and DE
− Supports Progressive
− Input data format (from VSPD): RGB888, RGB666
− Output data format: same as Input data format
− Supporting Full HD (1920 pixels x 1080 lines) for MIPI-DSI Output
− Supporting WXGA (1280 pixels x 800 lines) for Parallel Output

This patch documents the DU module found on RZ/G2L LCDC.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20240218164840.57662-2-biju.das.jz@bp.renesas.com


Signed-off-by: Maxime Ripard <mripard@kernel.org>