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/include/configs/MPC8641HPCN.h b/include/configs/MPC8641HPCN.h
index aca2ecc..7e91e64 100644
--- a/include/configs/MPC8641HPCN.h
+++ b/include/configs/MPC8641HPCN.h
@@ -146,6 +146,8 @@
     #define CFG_DDR_CS5_BNDS	0x00000FFF	/* Not done */
 #endif
 
+#define CFG_ID_EEPROM	1
+#define ID_EEPROM_ADDR 0x57
 
 /*
  * In MPC8641HPCN, allocate 16MB flash spaces at fe000000 and ff000000.