ANDROID: cpuhp: pause: reduce running priority pause/resume

In order to get a responsive pause operation, the resume/pause_cpus
are usually called within a RT task prio.

However only the lazy-resume and lazy-pause operations need to
happen quickly, the rest can happen at leisure. Running that
portion at high priority keeps the cpu away from important tasks.

Reduce the priority right after the lazy portion, and restore
it before returning, if it was at RT prio.

Bug: 203115740
Fixes: 683010f5 ("ANDROID: cpu/hotplug: add pause/resume_cpus interface")
Change-Id: I1f3394eb9b5fa1876330fef6e25a203da0fde670
Signed-off-by: Stephen Dickey <dickey@codeaurora.org>