drivers: dev_freq: Add frequency floor mitigation support

Thermal core framework supports governors that may place a
floor mitigation vote for a cooling device. Add support to devfreq
cooling device to place floor state mitigation on a device managed by
devfreq framework.

Change-Id: Iae15bd16b805013db98600746d92db9d17a4f8a9
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>