igc: Use hardware routine for PHY reset

Summary:
The previously used software reset routine wasn't sufficient
to reset the PHY if the bootloader hadn't left the device in
an initialized state. This was seen with the onboard igc port
on an 11th-gen Intel NUC.

The software reset isn't used in the Linux driver so all related
code has been removed.

Tested on: Netgate 6100 onboard ports, a discrete PCIe I225-LM card,
and an 11th-gen Intel NUC.

Reported by: woodsb02
Tested by: woodsb02 (NUC)
MFC after: 3 days
Sponsored by: Rubicon Communications, LLC ("Netgate")
Reviewed by: kbowling
Differential Revision: https://reviews.freebsd.org/D32772