dt_bindings: mfd: Add ROHM BD9576MUF and BD9573MUF PMICs

Add bindings for ROHM BD9576MUF and BD9573MUF PMICs. These
PMICs are primarily intended to be used to power the R-Car series
processors. They provide 6 power outputs, safety features and a
watchdog with two functional modes.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>