thermal: of: Extend of-thermal.c to provide number of trip points

This patch extends the of-thermal.c to provide information about number of
available trip points.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>
(cherry picked from commit 08dab66ec8431a1f744596cfc9f5fb659b623835)
Signed-off-by: Kevin Hilman <khilman@linaro.org>