ARM: 7038/1: mach-davinci: move GPIO driver to GPIO subsystem

As per example from the other ARM boards, push the DaVinci GPIO
driver down to the GPIO subsystem so it can be consolidated.

Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Kevin Hilman <khilman@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>