drivers: thermal: Add ftrace events for LMH DCVSh mitigation

LMH DCVSh driver receives interrupt from hardware whenever there is a
new mitigation frequency decision is made in hardware.

Add ftrace event to print the hardware mitigation frequency value from
driver.

Change-Id: Ib357ee3c3a461613bfd1268ec8f98973c2982c10
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>