lantiq: drop ath9k device tree binding & ath9k pci fixup

Due to the addition of the bindings to the ath9k driver, this code
isn't used any longer. The fixup is now done by the owloader.

Rename the ath_eep.c file to ath5k_eep.c to indicate that this files
includes ath5k related code only.

Signed-off-by: Mathias Kresin <dev@kresin.me>