pci: Add pci_find_base_class_from()

[Why]
linuxkpi needs to export pci_get_base_class() for DRM drivers from
Linux 6.7.

[How]
This new function searches a PCI device with the given base class and
returns it, regardless of its subclass.

The behavior is the same as pci_find_class_from() but the subclass is
ignored.

Reviewed by: manu
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D48745