net: fec: enable regulator for fec phy

If bootloader or platform initialization code does not enable the
power supply to fec phy, we need to do it in fec driver before calling
fec_reset_phy to have the phy powered on.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>