boards: renesas: Add MBOX support for Renesas RZ/V2L

Add MBOX support for board Renesas RZ/V2L-SMARC

Signed-off-by: Phuc Pham <phuc.pham.xr@bp.renesas.com>
Signed-off-by: Tien Nguyen <tien.nguyen.zg@renesas.com>