ARM: imx: select syscon for IMX6SL

This is required for building a kernel that enables only
IMX6SL but not IMX6Q, which would get a build error when
syscon is not available.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
diff --git a/arch/arm/mach-imx/Kconfig b/arch/arm/mach-imx/Kconfig
index de1bc91..60661a4 100644
--- a/arch/arm/mach-imx/Kconfig
+++ b/arch/arm/mach-imx/Kconfig
@@ -824,6 +824,7 @@
 	select HAVE_IMX_GPC
 	select HAVE_IMX_MMDC
 	select HAVE_IMX_SRC
+	select MFD_SYSCON
 	select PINCTRL
 	select PINCTRL_IMX6SL
 	select PL310_ERRATA_588369 if CACHE_PL310