PM / devfreq: Make update_devfreq() public

Currently update_devfreq() is only visible to devfreq governors outside
of devfreq.c. Make it public to allow drivers that adjust devfreq policies
to cause a re-evaluation of the frequency after a policy change.

Change-Id: I629c39eaa441a4d1cb675f73f0efb679e7a9e702
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Patch-mainline: linux-pm @ 14/6/18, 12:47
Signed-off-by: Akhil P Oommen <akhilpo@codeaurora.org>
Signed-off-by: Sharat Masetty <smasetty@codeaurora.org>