avr32: Fix GPIO initcall breakage

Add essential system devices, including GPIO controllers, automatically
at core_initcall time. This ensures that the devices are there when the
PIO driver gets initialized at postcore_initcall, fixing a bug exposed
by commit d6634db8fe "avr32: Use
platform_driver_probe for pio platform driver".

Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>

arch/avr32/boards/atngw100/setup.c

@@ -172,8 +172,6 @@ static int __init atngw100_init(void)
 	 * reserve any pins for it.
 	 */
 
-	at32_add_system_devices();
-
 	at32_add_device_usart(0);
 
 	set_hw_addr(at32_add_device_eth(0, &eth_data[0]));