at91: Add driver-model GPIO devices for AT91SAM9G45

Add these definitions so that GPIOs can be used with driver model.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
Tested-on: smartweb, corvus, taurus, axm
Tested-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Andreas Bießmann <andreas@biessmann.org>