This is part of the work making gpio.c generic enough, the changes
include:

1. move IRQ handling of GPIO 0 and 1 outside (and back into irq.c)

2. pxa_init_gpio() accepts a range for muxed GPIO IRQs, and an IRQ
   number for the muxed GPIOs

3. __gpio_is_occupied() and __gpio_is_inverted() are made inline,
   and are moved into <mach/gpio.h> instead of generic gpio.c

Signed-off-by: Eric Miao <eric.miao@marvell.com>