trace/irq: sched: irq trace events should be used with !PROVE_LOCKING

When enabling PROVE_LOCKING, kernel build fails due to undefined symbol
error for the irqsoff_tracing_threshold_ns which is used in sysctl
interface,sysctl_irqsoff_tracing_threshold_ns. As per PREEMPTIRQ_EVENTS
Kconfig help, for tracing irq disable/enable events CONFIG_PROVE_LOCKING
should be disabled. This commit fixes by making the proc entry under
the PROVE_LOCKING config.

Change-Id: Ie28afd31013a9c393f32ad328cedfc0517867fc4
Signed-off-by: Yadu MG <ymg@codeaurora.org>