libqos/ahci: create libqos/ahci.c

With global state removed, code responsible for booting up,
verifying, and initializing the AHCI HBA is extracted and
inserted into libqos/ahci.c, which would allow for other
qtests in the future to quickly grab a meaningfully initialized
reference to an AHCI HBA.

Even without other users, functionalizing and isolating the code
assists future AHCI tests that exercise Q35 migration.

For now, libqos/ahci.o will be PC-only, but can be expanded into
something arch-agnostic in the future, if needed.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1421698563-6977-16-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
