net: macb: allow deffered probe of the driver

The driver is trying to acquire clocks which maybe
are not available yet. Allow the driver to request
deffered probe by providing a probe function and
registering it with module_platform_driver. [1]
This patch is based on 3.19-rc5.

[1] https://lkml.org/lkml/2013/9/23/118

Signed-off-by: Nicolae Rosia <nicolae.rosia@certsign.ro>
Signed-off-by: David S. Miller <davem@davemloft.net>