pmic: raa215300: Bind sysreset driver

If SYSRESET support is enabled for the RAA215300 PMIC, we need to bind
the raa215300_sysreset driver as a child device of the PMIC.

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