ARM: Orion: Add arch support needed for I2C via DT.

The MV64XXX I2C driver needs a clock in order to calculate the baud
rate factors. So add an clk to the clk tree. Also add the base DT
properties for kirkwood devices.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>

Conflicts:
	arch/arm/mach-kirkwood/common.c