MAINTAINERS: Add ROHM BD9576MUF and BD9573MUF drivers

Add maintainer entries for ROHM BD9576MUF and ROHM BD9573MUF drivers.
MFD, regulator and watchdog drivers were introduced for these PMICs.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Lee Jones <lee.jones@linaro.org>