ixp4xx: fix compilation by adding gpiolib support

Once again, ixp4xx no longer even compiles. This patch fixes the issue
by converting over to gpiolib. This patch was first made by Imre and
posted by Marc, and I added in Russell's suggestion to empty the gpio
header file.

This fix should also go for 3.1, 3.2, 3.3, and 3.4.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>