ACPI: Make it compile on architectures other than x86.

Change-Id: Ie72dd2c6a571234399dc99d3573a5de19252737e
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5269
Reviewed-by: Fredrik Holmqvist <fredrik.holmqvist@gmail.com>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>