thermal: of: improve of-thermal sensor registration API
Different drivers request API extensions in of-thermal. For this reason,
additional callbacks are required to fit the new drivers needs.
The current API implementation expects the registering sensor driver
to provide a get_temp and get_trend callbacks as function parameters.
As the amount of callbacks is growing, this patch changes the existing
implementation to use a .ops field to hold all the of thermal callbacks
to sensor drivers.
This patch also changes the existing of-thermal users to fit the new
API design. No functional change is introduced in this patch.