net: freescale: fec: Fix ethtool -d runtime PM

In order to dump the FECs registers the clocks have to be ticking,
otherwise a data abort occurs.  Add calls to runtime PM so they are
enabled and later disabled.

Fixes: e8fcfcd5 ("net: fec: optimize the clock management to save power")
Reported-by: Chris Healy <Chris.Healy@zii.aero>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>