MAINTAINERS: bd70528: Drop ROHM BD70528 drivers

The only known BD70528 use-cases are such that the PMIC is controlled
from separate MCU which is not running Linux. I am not aware of
any Linux driver users. Furthermore, it seems there is no demand for
this IC.

Ease the maintenance burden and drop the driver.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/90b0565c0eb9429b0962f08d45292a5a9ebe5cea.1637066805.git.matti.vaittinen@fi.rohmeurope.com