fec: Place the phy regulator in the private structure

Instead of using a local reg_phy structure, let's put it inside the private
structure, so that we are able to have access to the regulator structure even
when we are outside fec_probe().

This is in preparation for controlling the FEC PHY regulator in the suspend and
resume functions.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>