thunderbolt: Support generic USB4 NHIs

Check a PCI device's class, subclass, and progif to figure out if it is
a USB4 NHI. nhi_identifiers is completely removed as only these generic
USB4 NHIs are supported anyway, and all remnants of ICM-supporting code
are removed too. All devices now use the HCM.

PR: 290827
Reviewed by: jhb, ngie
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D52861