davinci: da850evm: Make EEPROM MAC code configurable

There was a check for CONFIG_MAC_ADDR_IN_EEPROM and
a check for CONFIG_MAC_ADDR_IN_SPIFLASH, however
some of the EEPROM related code wasn't encapsulated
inside the #if defined statement so the EEPROM code
could get executed even when it wasn't explicitly
enabled or wanted.

Signed-off-by: Adam Ford <aford173@gmail.com>