arm/imx21: add kbuild support for the Freescale i.MX21

* adds Kconfig variables
* specifies different physical address for i.MX21 because of the
  different memory layouts
* disables support for UART5/UART6 in the i.MX serial driver
  (the i.MX21 doesn't have those modules)

Based on code from "Martin Fuzzey" <mfuzzey@gmail.com>

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
diff --git a/arch/arm/mach-mx2/Kconfig b/arch/arm/mach-mx2/Kconfig
index 1eaa97c..412d2d5 100644
--- a/arch/arm/mach-mx2/Kconfig
+++ b/arch/arm/mach-mx2/Kconfig
@@ -1,12 +1,25 @@
 comment "MX2 family CPU support"
 	depends on ARCH_MX2
 
+choice
+	prompt "MX2 Type"
+	depends on ARCH_MX2
+	default MACH_MX21
+
+config MACH_MX21
+	bool "i.MX21 support"
+	depends on ARCH_MX2
+	help
+	  This enables support for Freescale's MX2 based i.MX21 processor.
+
 config MACH_MX27
 	bool "i.MX27 support"
 	depends on ARCH_MX2
 	help
 	  This enables support for Freescale's MX2 based i.MX27 processor.
 
+endchoice
+
 comment "MX2 Platforms"
 	depends on ARCH_MX2