net: fec: remove the unused functions

Removed those unused functions since we simplified the driver
by using the page pool to manage RX buffers.

Signed-off-by: Shenwei Wang <shenwei.wang@nxp.com>
Link: https://lore.kernel.org/r/20221017161236.1563975-1-shenwei.wang@nxp.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>