dt-bindings: Add RZ/G2L CPG bindings

Import bindings for the Clock Pulse Generator (CPG) module in the
Renesas RZ/G2L SoC family.

This patch is based on the dt-bindings in Linux v6.5
(commit 52e12027d50affbf60c6c9c64db8017391b0c22e).

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>