sunxi: board: Move USB ethernet initialization to board_late_init()

For the sake of consistency (*) and order of initialization, i.e.
after we have got the ethernet address, interrupt and timer initialized,
try to initialize USB ethernet gadget.

*) for example, zynqmp uses same order.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Tested-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>