ARM: 7083/1: rewrite U300 GPIO to use gpiolib

This rewrites the U300 GPIO so as to use gpiolib and
struct gpio_chip instead of just generic GPIO, hiding
all the platform specifics and passing in GPIO chip
variant as platform data at runtime instead of the
compiletime kludges.

As a result <mach/gpio.h> is now empty for U300 and
using just defaults.

Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Debian kernel maintainers <debian-kernel@lists.debian.org>
Cc: Arnaud Patard <arnaud.patard@rtp-net.org>
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>