powerpc: Disable IRQs off tracer in ppc64 defconfig

The IRQs off tracer enables mcount which has a big impact on
performance. Disable it.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/configs/ppc64_defconfig

@@ -446,7 +446,6 @@ CONFIG_DEBUG_MUTEXES=y
 # CONFIG_RCU_CPU_STALL_DETECTOR is not set
 CONFIG_LATENCYTOP=y
 CONFIG_SYSCTL_SYSCALL_CHECK=y
-CONFIG_IRQSOFF_TRACER=y
 CONFIG_SCHED_TRACER=y
 CONFIG_BLK_DEV_IO_TRACE=y
 CONFIG_DEBUG_STACKOVERFLOW=y