cpufreq: Adding traces to the cpufreq

Logging the following events in ondemand for debugging purposes:
1) When thread migration of a foreground event triggers frequency
   synchronization of destination cpu with the source cpu.
2) Ondemand sampling instant when cpu load is evaluated and an
   appropriate frequency is selected corresponding to the load.

Change-Id: I44341c660b66135943f235d467090e3cc863a2fb
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>