drivers: thermal: reintroduce notifier for max level transitions

commit 547ecd3b
("drivers: thermal: cpu_cooling: Add a notifier for max level transitions")
introduced notifier for max level transitions earlier, later, thermal
drivers got refractored and removed chunk of code that was introduced
to support notifier for max level transitions. Bringing back the code
that was removed on top of refactored thermal code.

Change-Id: Ifeb3a73a074d04f88e81f1d62dc4aecb51ef3cec
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>