net: fec: add fec_txq_trigger_xmit() helper

Currently, the workaround for FEC_QUIRK_ERR007885 has three call sites,
so add the helper fec_txq_trigger_xmit() to make the code more concise
and reusable.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260205085742.2685134-2-wei.fang@nxp.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>