Attach com over acpi on amd64. Some hardware uses a different interrupt

Attach com over acpi on amd64. Some hardware uses a different interrupt
assignment compared to the the legacy one supported by com over isa.
This causes the console to halt once userland takes over as no
interrupts are received. The actual address and irq can be read from
ACPI, kettenis@ already added support for arm64 which paved the way for
amd64.

Some consoles that previously attached over isa are now expected to
attach over acpi.

Thanks to patrick@ for testing on arm64.

ok kettenis@