net: allwinner: emac: Add missing free_irq

The sun4i-emac driver uses devm_request_irq at .ndo_open time, but relies on
the managed device mechanism to actually free it. This causes an issue whenever
someone wants to restart the interface, the interrupt still being held, and not
yet released.

Fall back to using the regular request_irq at .ndo_open time, and introduce a
free_irq during .ndo_stop.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: stable@vger.kernel.org # 3.11+
Signed-off-by: David S. Miller <davem@davemloft.net>