sysreset: Support reset via Renesas RAA215300 PMIC

This patch adds support for resetting a board via the RAA215300 PMIC.

Note that the RAA215300 documentation names the available reset types
differently to u-boot:

  * A "warm" reset via the RAA215300 PMIC will fully reset the SoC
    (CPU & GPIOs), so this corresponds to SYSRESET_COLD.

  * A "cold" reset via the RAA215300 PMIC will cycle all power supply
    rails, so this corresponds to SYSRESET_POWER.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>