MIPS: BCM63xx: Move bcm63xx_gpio_init() to bcm63xx_register_devices().
When called from prom init code, bcm63xx_gpio_init() will fail as it
will call gpiochip_add() which relies on a working kmalloc() to alloc
the gpio_desc array and kmalloc is not useable yet at prom init time.
Move bcm63xx_gpio_init() to bcm63xx_register_devices() (an
arch_initcall) where kmalloc works.