cpufreq: interactive: Revert sync on thread migration optimizations

Commit f8b27656
(cpufreq: Sync on thread migration optimizations) is no longer needed
for targets with synchronous CPUs.

Part of that commit has already been reverted in
a913b3af
(cpufreq: interactive: Revert timer start modification)

This commit reverts the remaining changes.

Change-Id: I7eadeb7e48cfbef8fec74eb1b0e221eb65482f52
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>