We don't have actual drivers for serial in:
This leads to falling back to legacy 16550A interface, legacy since 1995
Vendor firmware exposes it as PNP0501, but that's not nearly enough to reliably identify it.
For National Semiconductors parts (and derivatives) PC87108 datasheet can be used for reference, and it appears to be a probable introduction of said controller (1995), with first SuperIOs incorporating it next year (PC87308/PC87338)
Previous upstreaming attemps by Pavel Machek (1998-2000):
Location of prescaler register on modern Nuvoton EC/SIO: "CR F0h" :
Gigabyte board uses IT8718F which only has 16550A interfaces, so the way to debug that one would be to use: ne2k / ehci-debug / serial controller on PCI(e)