MIPS: BCM63xx: Fix double gpio registration.

bcm63xx_gpio_init is already called from prom_init to allow board to use
them early, so we can remove the unneeded arch_initcall.

Signed-off-by: Maxime Bizon <mbizon@freebox.fr>
To: linux-mips@linux-mips.org
Cc: Maxime Bizon <mbizon@freebox.fr>
Patchwork: http://patchwork.linux-mips.org/patch/899/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>