devmatch: defer until after kld

devmatch loads a number of things automatically. Allow the list of
things to load to happen first in case those drivers affect what would
be loaded. Normally, this will produce the same results, but there's
some special cases that may not when drivers are loaded that report
other drivers missing, like virtio_pci.

PR: 253287
Reviewed by: imp
MFC After: 2 weeks