[ARM] MX1: Add missing selection of ARM920T

The MX1 only has one possible CPU type, ARM920T. Select it in
Kconfig.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
diff --git a/arch/arm/plat-mxc/Kconfig b/arch/arm/plat-mxc/Kconfig
index 16cb07cd..9cc2b16 100644
--- a/arch/arm/plat-mxc/Kconfig
+++ b/arch/arm/plat-mxc/Kconfig
@@ -8,6 +8,7 @@
 
 config ARCH_MX1
 	bool "MX1-based"
+	select CPU_ARM920T
 	help
 	  This enables support for systems based on the Freescale i.MX1 family