ANDROID: trace: Add WALT util signal to trace event sched_load_cfs_rq

WALT only operates on root rq. WALT is already intergated into the
trace event sched_load_se.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Change-Id: If9c50c87404bc712ac29e9a9a8b90f7eb1b254e2