We can't be using the MAC including the MDIO controller while the clocks
are off, but this is exactly the case when mdio_register is called and
the interface is not yet up. To allow reading the PHY id to succeed
before the interface is up, turn on the clocks as part of the
initialization in the probe.

This fixes following error at probe time:

    ERROR: <NULL>: MDIO not idle at entry

The NULL is fixed in a follow-up commit.

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>