at91_ether: request/free GPIO for PHY interrupt

When the at91_ether driver is using a GPIO for its PHY interrupt,
be sure to request (and later, if needed, free) that GPIO.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>