pxa/hx4700: Fix PXA_GPIO_IRQ_BASE/IRQ_NUM values

The hx4700 platform has 72 board gpios: 64 ASIC3 gpios numbered 192..255, and
8 EGPIO gpios numbered 256..263 (plus a 9th which is not used).
Thus the new CONFIG_ARCH_NR_GPIO config option must be set to 264.

Signed-off-by: Paul Parsons <lost.distance@yahoo.com>
Acked-by: Philipp Zabel <philipp.zabel@gmail.com>
Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>