lib: utils: serial: Add Renesas SCIF driver

Add Renesas SCIF driver.

Based on a patch in the BSP by Takeki Hamada
<takeki.hamada.ak@bp.renesas.com>
Link: https://github.com/renesas-rz/rz_opensbi/commits/work/OpenSBI-PMA



Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Anup Patel <anup@brainfault.org>