xtensa: no need to select USE_GENERIC_SMP_HELPERS

Commit f615136c ("xtensa: add SMP support") added "select
USE_GENERIC_SMP_HELPERS". But the Kconfig symbol USE_GENERIC_SMP_HELPERS
was already removed in v3.13, so that select is a nop. Drop it.
Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/Kconfig

@@ -134,7 +134,6 @@ config HAVE_SMP
 config SMP
 	bool "Enable Symmetric multi-processing support"
 	depends on HAVE_SMP
-	select USE_GENERIC_SMP_HELPERS
 	select GENERIC_SMP_IDLE_THREAD
 	help
 	  Enabled SMP Software; allows more than one CPU/CORE