igc: add support for frame preemption verification

This patch implements the "ethtool --set-mm" callback to trigger the
frame preemption verification handshake.

Uses the MAC Merge Software Verification (mmsv) mechanism in ethtool
to perform the verification handshake for igc.
The structure fpe.mmsv is set by mmsv in ethtool and should remain
read-only for the driver.

Other mmsv callbacks:
a) configure_tx() -> not used yet at this point
   - igc lacks registers to configure FPE in the transmit direction, so
     this API is not utilized for now. When igc supports preemptible queue,
     driver will use this API to manage its configuration.

b) configure_pmac() -> not used
   - this callback dynamically controls pmac_enabled at runtime. For
     example, mmsv calls configure_pmac() and disables pmac_enabled when
     the link partner goes down, even if the user previously enabled it.
     The intention is to save power but it is not feasible in igc
     because it causes an endless adapter reset loop:

   1) Board A and Board B complete the verification handshake. Tx mode
      register for both boards are in TSN mode.
   2) Board B link goes down.

   On Board A:
   3) mmsv calls configure_pmac() with pmac_enabled = false.
   4) configure_pmac() in igc updates a new field based on pmac_enabled.
      Driver uses this field in igc_tsn_new_flags() to indicate that the
      user enabled/disabled FPE.
   5) configure_pmac() in igc calls igc_tsn_offload_apply() to check
      whether an adapter reset is needed. Calls existing logic in
      igc_tsn_will_tx_mode_change() and igc_tsn_new_flags().
   6) Since pmac_enabled is now disabled and no other TSN feature is
      active, igc_tsn_will_tx_mode_change() evaluates to true because Tx
      mode will switch from TSN to Legacy.
   7) Driver resets the adapter.
   8) Registers are set, and Tx mode switches to Legacy.
   9) When link partner is up, steps 3-8 repeat, but this time with
      pmac_enabled = true, reactivating TSN.
      igc_tsn_will_tx_mode_change() evaluates to true again, since Tx
      mode will switch from Legacy to TSN.
  10) Driver resets the adapter.
  11) Adapter reset completes, registers are set, and Tx mode switches to
      TSN.

  On Board B:
  12) Adapter reset on Board A at step 10 causes it to detect its link
      partner as down.
  13) Repeats steps 3-8.
  14) Once reset adapter on Board A is completed at step 11, it detects
      its link partner as up.
  15) Repeats steps 9-11.

   - this cycle repeats indefinitely. To avoid this issue, igc only uses
     mmsv.pmac_enabled to track whether FPE is enabled or disabled.

Co-developed-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Co-developed-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
Signed-off-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
Co-developed-by: Chwee-Lin Choong <chwee.lin.choong@intel.com>
Signed-off-by: Chwee-Lin Choong <chwee.lin.choong@intel.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>