arch/xtensa: fix Kconfig typos for HAVE_SMP

Fix typos in xtensa Kconfig help text for HAVE_SMP.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: linux-xtensa@linux-xtensa.org
Message-Id: <500b2132-ea3c-a385-1f37-05664de5f1dd@infradead.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>