Add support for reading and writing mac addresses to or from ID EEPROM.

Added code for reading and writing Mac addresses to/from ID EEPROM(0x57).
With attached patch, we can use command "mac/mac read/mac save/"
to read and write EEPROM under u-boot prompt.

U-boot will calculate the checksum of EEPROM while bootup,
if it is right, then u-boot will check whether the mac address
of eTSEC0/1/2/3 is availalbe (non-zero).

If there is mac address availabe in EEPROM, u-boot will use it,
otherewise, u-boot will use the mac address defined in
MPC8641HPCN.h. This matches the requirement to set unique mac address
for each TSEC port.

Signed-off-by: Haiying Wang <haiying.wang@freescale.com>
Signed-off-by: York Sun <yorksun@freescale.com>
diff --git a/common/Makefile b/common/Makefile
index eb0b5da..a62bc16 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -51,7 +51,7 @@
 	  memsize.o miiphybb.o miiphyutil.o \
 	  s_record.o serial.o soft_i2c.o soft_spi.o spartan2.o spartan3.o \
 	  usb.o usb_kbd.o usb_storage.o \
-	  virtex2.o xilinx.o crc16.o xyzModem.o
+	  virtex2.o xilinx.o crc16.o xyzModem.o cmd_mac.o
 
 OBJS	= $(AOBJS) $(COBJS)