i2c: slave-eeprom: update documentation to recent changes

Support for 16-bit addresses has been added, so remove it from the todo
list. Also, in the introductory sentence, may clear we talk about "slave
IP cores" to make reading easier.

Fixes: 82d51481 ("i2c-eeprom_slave: Add support for more eeprom models")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>