ptp: ocp: add nvmem interface for accessing eeprom

Add the at24 drivers for the eeprom, and use the accessors
via the nvmem API instead of direct i2c accesses.  This makes
things cleaner.

Add an eeprom map table which specifies where the pre-defined
information is located.  Retrieve the information and and export
it via the devlink interface.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>