MX: set a common place to share code for Freescale i.MX

Up now only MX5 and MX6 can share code, because they have
a common source directory in cpu/armv7. Other not armv7
i.MX can profit of the same shared code. Move these files
into a directory accessible for all, similar to plat-mxc
in linux.

Signed-off-by: Stefano Babic <sbabic@denx.de>
diff --git a/Makefile b/Makefile
index e5f8d05..fe2f98c 100644
--- a/Makefile
+++ b/Makefile
@@ -306,11 +306,8 @@
 LIBS-y += $(CPUDIR)/omap-common/libomap-common.o
 endif
 
-ifeq ($(SOC),mx5)
-LIBS-y += $(CPUDIR)/imx-common/libimx-common.o
-endif
-ifeq ($(SOC),mx6)
-LIBS-y += $(CPUDIR)/imx-common/libimx-common.o
+ifneq (,$(filter $(SOC), mx25 mx27 mx5 mx6 mx31 mx35))
+LIBS-y += arch/$(ARCH)/imx-common/libimx-common.o
 endif
 
 ifeq ($(SOC),s5pc1xx)