ARM: Orion: Eth: Add clk/clkdev support.

The t_clk is moved from the shared part of the ethernet driver into
the per port section. Each port can have its own gated clock, which it
needs to enable/disable, as oppossed to there being one clock shared
by all ports. In practice, only kirkwood supports this at the moment.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Jamie Lentin <jm@lentin.co.uk>
Signed-off-by: Mike Turquette <mturquette@linaro.org>