pinctrl: pinctrl-pic32: Add PIC32 pin control driver

Add a driver for the pin controller present on the Microchip PIC32
including the specific variant PIC32MZDA. This driver provides pinmux
and pinconfig operations as well as GPIO and IRQ chips for the GPIO
banks.

Signed-off-by: Joshua Henderson <joshua.henderson@microchip.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>