imx: Introduce CONFIG_MACH_IMX

Currently, there is no over-arching symbol for access to
arch/arm/mach-imx nor the CONFIG symbols that are common over all of
these related platforms.  This new CONFIG symbol will allow us to start
down this path.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/mach-imx/Kconfig b/arch/arm/mach-imx/Kconfig
index 653463a..c5923e3 100644
--- a/arch/arm/mach-imx/Kconfig
+++ b/arch/arm/mach-imx/Kconfig
@@ -1,3 +1,6 @@
+config MACH_IMX
+	bool
+
 config HAS_CAAM
 	bool