ARM: imx6ul: Add support for liteSOM

liteSOM is a System On Module (http://grinn-global.com/litesom/). It
can't exists on its own, but will be used as part of other boards.

Hardware specification:
 * NXP i.MX6UL processor
 * 256M or 512M DDR3 memory
 * optional eMMC (uSDHC2)

Here we treat SOM similar to SOC, so we place it inside arch/arm/mach-*
directory and make it possible to reuse initialization code (i.e. DDR,
eMMC init) for all boards that use it.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 714dd8b..c655963 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -900,6 +900,8 @@
 
 source "arch/arm/mach-kirkwood/Kconfig"
 
+source "arch/arm/mach-litesom/Kconfig"
+
 source "arch/arm/mach-mvebu/Kconfig"
 
 source "arch/arm/cpu/armv7/ls102xa/Kconfig"