puc has preferred MSI for every card since MSI support was added, with
only a global tunable to opt out. uart(4) makes the same decision for
the serial devices it attaches directly, and has since grown two
defences: it skips MSI unless the device advertises exactly one vector,
because attaching a single instance to a device offering many has caused
problems (PR 235016), and it lets individual devices be flagged when
they claim MSI support that does not work.

Adopt both.