dt-bindings: dma: rz-dmac: Add conditional schema for RZ/G3L

The RZ/G3L DMA controller is compatible with RZ/G2L, sharing the same
IP. However, the conditional schema logic that enforces RZ/G2L-specific
binding constraints was not extended to cover the RZ/G3L compatible
string, leaving its bindings without proper validation.

Add the RZ/G3L compatible string to the existing RZ/G2L conditional
schema so that the same property constraints are applied to both SoCs.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Fixes: e45cf0c7d9b960f1 ("dt-bindings: dma: rz-dmac: Document RZ/G3L SoC")
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260306145819.897047-1-biju.das.jz@bp.renesas.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>