ARM: 7042/3: mach-ep93xx: break out GPIO driver specifics

The <mach/gpio.h> file is included from upper directories
and deal with generic GPIO and gpiolib stuff. Break out the
platform and driver specific defines and functions into its own
header file.

Cc: Ryan Mallon <rmallon@gmail.com>
Acked-by: Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>