nios2: Move serial drivers to individual files in  drivers/serial

   The standard Altera UART & JTAG UART as well as the OpenCores
   YANU driver are now in individual files in drivers/serial
   rather than a single file uner cpu/nios2.

Signed-off-by: Scott McNutt <smcnutt@psyent.com>
diff --git a/cpu/nios2/Makefile b/cpu/nios2/Makefile
index 75f30b4..3dfaa83 100644
--- a/cpu/nios2/Makefile
+++ b/cpu/nios2/Makefile
@@ -27,7 +27,7 @@
 
 START	= start.o
 SOBJS	= exceptions.o
-COBJS	= cpu.o interrupts.o serial.o sysid.o traps.o epcs.o
+COBJS	= cpu.o interrupts.o sysid.o traps.o epcs.o
 
 SRCS	:= $(START:.o=.S) $(SOBJS:.o=.S) $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(SOBJS) $(COBJS))