drivers: serial: Add support for RZ/T2M

Add serial driver support for Renesas RZ/T2M

Signed-off-by: Hieu Nguyen <hieu.nguyen.ym@bp.renesas.com>
Signed-off-by: Nhut Nguyen <nhut.nguyen.kc@renesas.com>
Signed-off-by: Binh Nguyen <binh.nguyen.xw@renesas.com>