dt-bindings: mfd: syscon: Document the LVDS_CMN syscon for the RZ/G3L

dt-bindings: mfd: syscon: Document the LVDS_CMN syscon for the RZ/G3L

The RZ/G3{E,L} SoCs have an LVDS Common (LVDS_CMN) region which is common
to all LVDS channels. The RZ/G3L has single-link, but the RZ/G3E has both
single and dual-link.

Use the syscon interface to access these registers for scalability.

Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20260421172910.218497-2-biju.das.jz@bp.renesas.com
Signed-off-by: Lee Jones <lee@kernel.org>