thermal: of: Extend current of-thermal.c code to allow setting emulated temp

Before this change it was only possible to set get_temp() and get_trend()
methods to be used in the common code handling passing parameters via
device tree to "cpu-thermal" CPU thermal zone device.

Now it is possible to also set emulated value of temperature for debug
purposes.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Acked-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>