thermal: Add generic cpufreq cooling implementation

This patch adds support for generic cpu thermal cooling low level
implementations using frequency scaling up/down based on the registration
parameters. Different cpu related cooling devices can be registered by the
user and the binding of these cooling devices to the corresponding
trip points can be easily done as the registration APIs return the
cooling device pointer. The user of these APIs are responsible for
passing clipping frequency . The drivers can also register to recieve
notification about any cooling action called. Even the driver can effect
the cooling action by modifying the default data such as freq_clip_max if
needed.

Signed-off-by: Amit Daniel Kachhap <amit.kachhap@linaro.org>