mips_malta: generate SMBUS EEPROM data

The malta contains 2 EEPROMs, one containing SPD data for the SDRAM and
another containing board information such as serial number and MAC
address. These are both exposed via the PIIX4 SMBUS. Generating this
data and providing it to smbus_eeprom_init will allow YAMON to read a
serial number for the board and prevent it from warning that the EEPROM
data is invalid.

We already have the contents of the SPD EEPROM which are exposed via
FPGA I2C accesses, this is provided as part of the SMBUS EEPROM data
too for consistency.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
