uart: Match simple comm

Match the PCI simple comm devices (or try to). Be conservative and use
legacy interrupts rather than msi messages by default for this 'catch
all' since it matches what Linux does (it has opt-in generally for MSI,
but also matches more devices because it does a catch-all like
implemented in this commit).

Sponsored by: Netflix
Reviewed by: kbowling
Differential Revision: https://reviews.freebsd.org/D32228