sched, perf: MAINTAINERS update, add submaintainers and reviewers

The below entries are a little unorthodox; I've not found other entries in
MAINTAINER that subdivide responsibilities like this, and certainly the lovely
get_maintainers.pl script will not get it, but I'm thinking to a human it
should be plenty clear and we're all very good at ignoring email anyway.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>