ANDROID: sched/events: Introduce rt_rq load tracking trace event

We want to be able to track rt_rq signals same as we do for other RQs.

Signed-off-by: Chris Redpath <chris.redpath@arm.com>
(cherry-picked from commit 574a2d189695c334ae290f522b098f05398a3765)
[ - Fixed conflicts with the refactored RT util_avg tracking
  - Changed commit title for consistency with other tracepoint patches ]
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
Change-Id: I38b64baa50e1ff86019ca4b8b0a04af994880b35