[POWERPC] Fix kernel panic in arch_arm_kprobe

The code in arch_arm_kprobe was trying to set a breakpoint which
resulted in a page fault because the kernel text pages were write
protected.  Disable the write protect when CONFIG_KPROBES is defined.
Signed-off-by: Ionut Nicu <ionut.nicu@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

include/asm-powerpc/pgtable-ppc32.h

@@ -420,7 +420,8 @@ extern int icache_44x_need_flush;
 #define _PAGE_IO	(_PAGE_KERNEL | _PAGE_NO_CACHE | _PAGE_GUARDED)
 #define _PAGE_RAM	(_PAGE_KERNEL | _PAGE_HWEXEC)
 
-#if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || defined(CONFIG_BDI_SWITCH)
+#if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || defined(CONFIG_BDI_SWITCH) ||\
+	defined(CONFIG_KPROBES)
 /* We want the debuggers to be able to set breakpoints anywhere, so
  * don't write protect the kernel text */
 #define _PAGE_RAM_TEXT	_PAGE_RAM