drivers: thermal: Add support to handle cooling device floor

Some silicons operating at low temperatures outside of its operating
temperature range need to increase the supply voltage for timing
closure. In order to achieve this, the cooling device should be able to
place an operating floor mitigation on a cooling device.

Add new optional callbacks in the framework for the cooling device to
register if they support placing a floor mitigation. These two callbacks
will be used by thermal core framework to set and get the current floor
request. Also add support in thermal sysfs to set and get the floor request
from userspace. Thermal framework aggregates the floor requests from
multiple thermal zones and then notifies the cooling device.

Change-Id: I4a01e46c8e576a41e1cb5c1f8e479b1a68fc8003
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>