ARM: Kirkwood: Ensure runit clock always ticks.

Marvell engineers tell us:

	It seems that many units use the RUNIT clock.
	SPI, UART, NAND, TWSI, ...
	So it's not possible to clock gate it.

Currently the SPI, NAND and TWSI driver will clk_prepaure_enable()
this clk, but since we have no idea what ... is, and turning this clk
off results in a hard lock, unconditionally enable runit.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Simon Baatz <gmbnomis@gmail.com>