[ARM] 4438/1: PXA: remove #ifdef .. #endif from pxa_gpio_demux_handler()

1. use GPIO_IRQ_mask[] to select those bits of interest, actually
   only those "unmasked" GPIO IRQs with their corresponding bits
   in GPIO_IRQ_mask[] set to "1" should be checked

2. remove #ifdef PXA_LAST_GPIO > 96 .. #endif, GPIO_IRQ_mask[]
   is used to mask out the irrelevant bits, so that even though
   the GEDR3 on PXA25x is reserved, it will be masked, and the
   following code will never run. Another point is that GPIO85-
   GPIO95 bits within GEDR2 will also be masked out on PXA25x

Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>