pinctrl: renesas: Add RZ/G2L PFC driver

This driver adds support for the pinctrl features of the GPIO/PFC module
in the Renesas RZ/G2L (R9A07G044) SoC.

A multi-function `rzg2l-pfc` driver is defined for UCLASS_NOP, which
binds the `rzg2l-pfc-pinctrl` UCLASS_PINCTRL driver dynamically. We also
define common macros and functions for the PFC in <renesas/rzg2l-pfc.h>.
This makes it easy to add an additional UCLASS_GPIO driver for the GPIO
functionality of this module in a follow-up patch.

This patch is based on the corresponding Linux v6.5 driver
(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>