ARM: keystone: select ARM_ERRATA_798181 only for SMP

Selecting this symbol causes a build warning without SMP:

warning: (ARCH_KEYSTONE) selects ARM_ERRATA_798181 which has unmet direct dependencies (CPU_V7 && SMP)
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NSantosh Shilimkar <santosh.shilimkar@ti.com>

arch/arm/mach-keystone/Kconfig

@@ -9,7 +9,7 @@ config ARCH_KEYSTONE
 	select GENERIC_CLOCKEVENTS
 	select HAVE_SCHED_CLOCK
 	select ARCH_WANT_OPTIONAL_GPIOLIB
-	select ARM_ERRATA_798181
+	select ARM_ERRATA_798181 if SMP
 	help
 	  Support for boards based on the Texas Instruments Keystone family of
 	  SoCs.