arm: at91: at91sam9x5: fix gpio number per bank

On the at91sam9x5 SoC series, GPIO banks B and D only have 19 and 22
pins. So add a property to set this parameter.

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