at91: regroup gpio and pinctrl under the same ranges

Fix also the reg size as we have 512 bytes bank not 256 bytes per gpio/mux
controller

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>