fsl: verify writes to the MAC address EEPROM

fsl: verify writes to the MAC address EEPROM

Update the code which writes to the on-board EEPROM so that it can detect if
the write failed because the EEPROM is write-protected.  Most of the 8xxx-class
Freescale reference boards use an AT24C02 EEPROM to store MAC addresses and
similar information.  With this patch, if the EEPROM is protected, the
"mac save" command will display an error message indicating that the write
has not succeeded.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>