Not all orion platforms can gate the clock, but if it does exist,
enable/disable it as appropriate.

v2: Fix the name of the clkdev entry.
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Tested-by: NJamie Lentin <jm@lentin.co.uk>
Signed-off-by: NMike Turquette <mturquette@linaro.org>