qcom-cpufreq: Remove save/restore of scheduling policy

Different structures might need to be saved and restored based on
different scheduling policies of current thread. Saving and restoring
priority using scheduler APIs is very fragile due to potential changes
in scheduler code. In addition, the priority change doesn't
provide any starvation guarantee because threads can be preempted
before the priority change.

Therefore remove save and restore of priority to avoid potential bugs
when scheduler API changes. Caller will now be responsible for setting
the right priority for their CPU frequency scaling workqueue/thread.

Change-Id: I2a5d8599e75c0c4aa902df3214c17ab2b13dc9a9
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>