powerpc: Turn off verbose debug output in powermac platform functions

This is along the lines suggested by Chris Lumens but goes further
in that it leaves the DEBUG symbol undefined, making the DBG macro
empty.

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/platforms/powermac/pfunc_base.c b/arch/powerpc/platforms/powermac/pfunc_base.c
index 4ffd2a9..9b7150f 100644
--- a/arch/powerpc/platforms/powermac/pfunc_base.c
+++ b/arch/powerpc/platforms/powermac/pfunc_base.c
@@ -9,7 +9,12 @@
 #include <asm/pmac_feature.h>
 #include <asm/pmac_pfunc.h>
 
+#undef DEBUG
+#ifdef DEBUG
 #define DBG(fmt...)	printk(fmt)
+#else
+#define DBG(fmt...)
+#endif
 
 static irqreturn_t macio_gpio_irq(int irq, void *data, struct pt_regs *regs)
 {