ARM: SMP depends on MMU

The SMP implementation on ARM heavily depends on MMU-only code.
As long as nobody is interested in fixing this, let's disable the
SMP option when building for nommu.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/Kconfig

@@ -1349,6 +1349,7 @@ config SMP
 		 MACH_REALVIEW_PB11MP || MACH_REALVIEW_PBX || ARCH_OMAP4 || \
 		 ARCH_EXYNOS4 || ARCH_TEGRA || ARCH_U8500 || ARCH_VEXPRESS_CA9X4 || \
 		 ARCH_MSM_SCORPIONMP || ARCH_SHMOBILE
+	depends on MMU
 	select USE_GENERIC_SMP_HELPERS
 	select HAVE_ARM_SCU if !ARCH_MSM_SCORPIONMP
 	help