cpufreq: interactive: Optimize sync_freq implementation

Don't let frequency drop below sync_freq if either load or
frequency among other cpus is above a certain threshold,
not necessarily both.

Change-Id: Iada28e08e812498e16d5189b309a7314f88814dd
cpufreq: interactive: Fix race in sync freq feature

When we switch to the interactive governor, the kernel will panic
because the policy object is NULL on affected cpus. Add a check to
avoid this situation.

Conflicts:
	drivers/cpufreq/cpufreq_interactive.c
cpufreq: interactive: fix merge error