acpi: Make nexus_acpi quiet on amd64 and i386

Otherwise during attach newbus prints "nexus0", which is not very
useful.

The generic nexus device is already quiet, as is nexus_acpi on arm64.

Sponsored by: The FreeBSD Foundation

(cherry picked from commit 732b69c9f9c84408e7e680a93ab91ce76ffef2ce)