libqos/ahci: add ahci_io

libqos/ahci: add ahci_io

ahci_io is a wrapper around ahci_guest_io that takes a pointer to host
memory instead, and will create a guest memory buffer and copy the data
to/from as needed and as appropriate for a read/write command, such that
after a read, the guest data will be in a host buffer, and for a write,
the data will be transmitted to guest memory prior to the block operation.

Now that we have all the syntactic sugar functions in place for AHCI,
we can convert the identify test to be very, very short.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1423158090-25580-17-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>