da850evm: read mac address from I2C EEPROM on AM18x EVM

add support to read mac address for AM18x EVM manufactured from
Spectrum digital which have mac address stored in I2C EEPROM manufactured
by WINBOND. This patch reads mac address from I2C EEPROM and sets the
environment variable if not set, If mac address is already present in
environment compare it with the mac address in EEPROM and warn on
mismatch.Introduced a config option CONFIG_MAC_ADDR_IN_EEPROM to where
to look for the mac address.

Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
Cc: Tom Rini <trini@ti.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Wolfgang Denk <wd@denx.de>
diff --git a/boards.cfg b/boards.cfg
index 5610daf..a61422b 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -120,7 +120,7 @@
 pm9g45                       arm         arm926ejs   pm9g45              ronetix        at91        pm9g45:AT91SAM9G45
 cam_enc_4xx                  arm         arm926ejs   cam_enc_4xx         ait            davinci     cam_enc_4xx
 da830evm                     arm         arm926ejs   da8xxevm            davinci        davinci
-da850_am18xxevm              arm         arm926ejs   da8xxevm            davinci        davinci     da850evm:DA850_AM18X_EVM
+da850_am18xxevm              arm         arm926ejs   da8xxevm            davinci        davinci     da850evm:DA850_AM18X_EVM,MAC_ADDR_IN_EEPROM,SYS_I2C_EEPROM_ADDR_LEN=2,SYS_I2C_EEPROM_ADDR=0x50
 da850evm                     arm         arm926ejs   da8xxevm            davinci        davinci     da850evm:MAC_ADDR_IN_SPIFLASH
 davinci_dm355evm             arm         arm926ejs   dm355evm            davinci        davinci
 davinci_dm355leopard         arm         arm926ejs   dm355leopard        davinci        davinci