ANDROID: sched/rt: schedtune: Add boost retention to RT

Boosted RT tasks can be deboosted quickly, this makes boost usless
for RT tasks and causes lots of glitching. Use timers to prevent
de-boost too soon and wait for long enough such that next enqueue
happens after a threshold.

While this can be solved in the governor, there are following
advantages:
- The approach used is governor-independent
- Reduces boost group lock contention for frequently sleepers/wakers
- Works with schedfreq without any other schedfreq hacks.

Bug: 30210506

Change-Id: I41788b235586988be446505deb7c0529758a9898
Signed-off-by: Joel Fernandes <joelaf@google.com>