wifi: ath9k: eeprom: remove platform data

There are no more board files defining platform data for this driver and
eeprom support through NVMEM has already been implemented. No need to
keep this old functionality around.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://patch.msgid.link/20240906195359.6982-2-rosenp@gmail.com