ahci: device queue implemented

Signed-off-by: Roni Häcki <roni.haecki@inf.ethz.ch>

Initial import of block device refactoring.

- Refactors existing AHCI code to use device queue interface.
- Adds harness test for disks.
- Adds some minor improvements for scalebench harness.
- Disable vtd due to some bug with the identity mapping on babybel machines.

Signed-off-by: Gerd Zellweger <mail@gerdzellweger.com>

Conflicts:
usr/acpi/acpi_main.c