ANDROID: sched/tune: fix sched_energy_diff tracepoint

sched_energy_diff tracepoint is in a place where it can never trace
payoff or nrg.delta. If CONFIG_SCHED_TUNE is enabled, put it in
a place where those values exist. If it is not enabled, trace from
the current location

Change-Id: Id5442f2b34ec76625491d27c0f4285433ca12699
Reported-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Signed-off-by: Quentin Perret <quentin.perret@arm.com>