ARM: Orion: PCIE: Add support for clk

Prepare and enable the clocks when the board indicates the pcie buses
will be used.

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