arm: mach-at91: move gpio.h to include folder

This commit add functions from mach-at91/gpio.h in include/mach/gpio.h.
This allow to use these functions outside the mach-at91 folder.

Signed-off-by: Raphaël Poggi <poggi.raph@gmail.com>
pinctrl: at91: add pinctrl driver

This driver is based on mach-at91/gpio.c and linux pinctrl driver.
The driver contains the gpio and pinctrl parts (like in linux) because the two parts
share some structures and logics.

Signed-off-by: Raphaël Poggi <poggi.raph@gmail.com>
ARM: AT91: move arch/arm/mach-at91/gpio.c functions to pinctrl driver

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>