MAINTAINERS: Add myself as designated reviewer of Intel PMIC GPIO

There are few Intel PMIC GPIO device drivers which I would like
to review.

Note, Intel MSIC is old system controller that based mostly on PMIC
integrated in it. Thus, I included it as well.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>