clk: renesas: Add CPG core wrapper for RZ/G2L SoC

Add CPG core wrapper for RZ/G2L family.

Based on a patch in the BSP by Binh Nguyen
<binh.nguyen.jz@renesas.com>.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20210609153230.6967-9-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>