libqos/ahci: Add ahci_port_check_interrupts helper

libqos/ahci: Add ahci_port_check_interrupts helper

A helper that compares a given port's current interrupts and checks them
against a supplied list of expected interrupt bits, and throws an error
if they do not match.

The helper then resets the requested interrupts on this port, and asserts
that the interrupt register is now empty.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1423158090-25580-7-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>