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: NArnd Bergmann <arnd@arndb.de>
Acked-by: NShawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/Kconfig

@@ -824,6 +824,7 @@ config SOC_IMX6SL
 	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