MIPS: AR7: Implement gpiolib

This patch implements gpiolib for the AR7 SoC.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/816/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>