net: stmmac: refactor FPE verification process

net: stmmac: refactor FPE verification process

Drop driver defined stmmac_fpe_state, and switch to common
ethtool_mm_verify_status for local TX verification status.

Local side and remote side verification processes are completely
independent. There is no reason at all to keep a local state and
a remote state.

Add a spinlock to avoid races among ISR, timer, link update
and register configuration.

This patch is based on Vladimir Oltean's proposal.

Vladimir Oltean says:

  ====================
  In the INITIAL state, the timer sends MPACKET_VERIFY. Eventually the
  stmmac_fpe_event_status() IRQ fires and advances the state to VERIFYING,
  then rearms the timer after verify_time ms. If a subsequent IRQ comes in
  and modifies the state to SUCCEEDED after getting MPACKET_RESPONSE, the
  timer sees this. It must enable the EFPE bit now. Otherwise, it
  decrements the verify_limit counter and tries again. Eventually it
  moves the status to FAILED, from which the IRQ cannot move it anywhere
  else, except for another stmmac_fpe_apply() call.
  ====================

Co-developed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Furong Xu <0x1207@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://patch.msgid.link/151f86c8428eba967039718c6bf90a7d841e703b.1725631883.git.0x1207@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>