regulator: dt-bindings: Add Renesas RAA215300 PMIC bindings

Document Renesas RAA215300 PMIC bindings.

The RAA215300 is a high Performance 9-Channel PMIC supporting DDR
Memory, with Built-In Charger and RTC.

It supports DDR3, DDR3L, DDR4, and LPDDR4 memory power requirements.
The internally compensated regulators, built-in Real-Time Clock (RTC),
32kHz crystal oscillator, and coin cell battery charger provide a
highly integrated, small footprint power solution ideal for
System-On-Module (SOM) applications. A spread spectrum feature
provides an ease-of-use solution for noise-sensitive audio or RF
applications.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/Message-Id

: <20230623140948.384762-2-biju.das.jz@bp.renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>