MAINTAINERS: Update entry for Intel Broxton PMC driver

The driver lives now under MFD so split the current entry into two parts
and add me as co-maintainer of the Intel Broxton PMC driver. While there
correct formatting of Zha Qipeng's email address.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>