[AVR32] Wire up USBA device

Implement at32_add_device_usba() and use it to wire up the USBA device
on ATSTK1000 and ATNGW100.

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

arch/avr32/boards/atngw100/setup.c

@@ -154,6 +154,7 @@ static int __init atngw100_init(void)
 	set_hw_addr(at32_add_device_eth(1, &eth_data[1]));
 
 	at32_add_device_spi(0, spi0_board_info, ARRAY_SIZE(spi0_board_info));
+	at32_add_device_usba(0, NULL);
 
 	for (i = 0; i < ARRAY_SIZE(ngw_leds); i++) {
 		at32_select_gpio(ngw_leds[i].gpio,