cpufreq: ondemand: Add duration for boosting

 * Keep default behavior of 500ms boost if "1" is given, otherwise use
   the value (microseconds) as the boost duration.

Change-Id: Id38adef1aece7b5609689e50d33cb11b74a352c5

Conflicts:

	drivers/cpufreq/cpufreq_ondemand.c