ARM: kill CONFIG_NEED_MACH_GPIO_H

The long pain of maintaining the legacy <mach/gpio.h> include
ladder is now gone with S5P as the last user being deleted. Cut
this Kconfig option and remove the inclusion directive in
<asm/gpio.h> for good.

Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>