powerpc: Minor cleanup to lib/Kconfig.debug

We don't need an explicit PPC64 in the DEBUG_PREEMPT dependancies as all
PPC platforms now support TRACE_IRQFLAGS_SUPPORT.
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

lib/Kconfig.debug

@@ -392,7 +392,7 @@ config DEBUG_KMEMLEAK_TEST
 
 config DEBUG_PREEMPT
 	bool "Debug preemptible kernel"
-	depends on DEBUG_KERNEL && PREEMPT && (TRACE_IRQFLAGS_SUPPORT || PPC64)
+	depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT
 	default y
 	help
 	  If you say Y here then the kernel will use a debug variant of the