cpufreq: interface for setting governor for a cpu

This implementation sets governor for a cpu using existing
cpufreq interfaces.

bug 871958

Change-Id: Ic4e7e2a2b0babaf1829b559b5db211666d449b86
Signed-off-by: Puneet Saxena <puneets@nvidia.com>
Reviewed-on: http://git-master/r/97939
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>