pinctrl: apple: add missing bits.h header

This is needed for the BIT(n) macro.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20211121165642.27883-5-joey.gouly@arm.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>