ppc4xx: Add support for 2nd I2C EEPROM on lwmon5 board

This patch adds support for the 2nd EEPROM (AT24C128) on the lwmon5
board. Now the "eeprom" command can be used to read/write from/to this
device. Additionally a new command was added "eepromwp" to en-/disable
the write-protect of this 2nd EEPROM.

The 1st EEPROM is not affected by this write-protect command.

Signed-off-by: Stefan Roese <sr@denx.de>