igc: Fix suspending when PTM is active

Some mainboard/CPU combinations, in particular, Alder Lake-S with a
W680 mainboard, have shown problems (system hangs usually, no kernel
logs) with suspend/resume when PCIe PTM is enabled and active. In some
cases, it could be reproduced when removing the igc module.

The best we can do is to stop PTM dialogs from the downstream/device
side before the interface is brought down. PCIe PTM will be re-enabled
when the interface is being brought up.

Fixes: a90ec848

 ("igc: Add support for PTP getcrosststamp()")
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Acked-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>