register at91_ether using platform_driver_probe

at91ether_probe lives in .init.text, so using platform_driver_register
to register it is wrong because binding a device after the init memory
is discarded (e.g. via sysfs) results in an oops.

As requested by David Brownell platform_driver_probe is used instead of
moving the probe function to .devinit.text as proposed initially.
This saves some memory, but devices registered after the driver is
probed are not bound (probably there are none) and binding via sysfs
isn't possible.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Andrew Victor <linux@maxim.org.za>
Signed-off-by: David S. Miller <davem@davemloft.net>