imx: move serial driver to drivers/serial

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/cpu/arm920t/imx/Makefile b/cpu/arm920t/imx/Makefile
index 9207ec1..d3352de 100644
--- a/cpu/arm920t/imx/Makefile
+++ b/cpu/arm920t/imx/Makefile
@@ -25,7 +25,7 @@
 
 LIB	= $(obj)lib$(SOC).a
 
-COBJS	= generic.o interrupts.o serial.o speed.o
+COBJS	= generic.o interrupts.o speed.o
 
 SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(SOBJS) $(COBJS))