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>

include/common.h

@@ -197,6 +197,9 @@ int	checkdram     (void);
 char *	strmhz(char *buf, long hz);
 int	last_stage_init(void);
 extern ulong monitor_flash_len;
+#ifdef CFG_ID_EEPROM
+int mac_read_from_eeprom(void);
+#endif
 
 /* common/flash.c */
 void flash_perror (int);