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.

Fixes: 14e85c0e ("gpio: remove gpio_descs global array")
Signed-off-by: Nicolas Schichan <nschichan@freebox.fr>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: Alexandre Courbot <acourbot@nvidia.com>
Patchwork: https://patchwork.linux-mips.org/patch/9530/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>