[PATCH] ppc64: update xmon helptext

xmon will do nothing but noise on a G5 if BOOTX_TEXT is not enabled.
mention the recognized kernel cmdline options for xmon.

Signed-off-by: Olaf Hering <olh@suse.de>
Cc: Paul Mackeras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>