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

The following trace event keys are mapped to:

 (1) load     : se->avg.load_avg

 (2) rbl_load : se->avg.runnable_load_avg

 (3) util     : se->avg.util_avg

To let this trace event work for configurations w/ and w/o group
scheduling support for cfs (CONFIG_FAIR_GROUP_SCHED) the following
special handling is necessary for non-existent key=value pairs:

 path = "(null)" : In case of !CONFIG_FAIR_GROUP_SCHED or the
                   sched_entity represents a task.

 comm = "(null)" : In case sched_entity represents a task_group.

 pid = -1        : In case sched_entity represents a task_group.

The following list shows examples of the key=value pairs in different
configurations for:

 (1) a task:

     cpu=0 path=(null) comm=sshd pid=2206 load=102 rbl_load=102  util=102

 (2) a taskgroup:

     cpu=1 path=/tg1/tg11/tg111 comm=(null) pid=-1 load=882 rbl_load=882 util=510

 (3) an autogroup:

     cpu=0 path=/autogroup-13 comm=(null) pid=-1 load=49 rbl_load=49 util=48

 (4) w/o CONFIG_FAIR_GROUP_SCHED:

     cpu=0 path=(null) comm=sshd pid=2211 load=301 rbl_load=301 util=265

The trace event is only defined for CONFIG_SMP.

The helper functions __trace_sched_cpu(), __trace_sched_path() and
__trace_sched_id() are extended to deal with sched_entities as well.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
[ Fixed issues related to the new pelt.c file ]
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
Change-Id: Id2e4d1ddb79c13412c80e4fa4147b9df3b1e212a