libata: add a host flag to ignore detected ATA devices

commit db63a4c8115a0bb904496e1cdd3e7488e68b0d06 upstream.

Where devices are visible via more than one host we sometimes wish to
indicate that cirtain devices should be ignored on a specific host.  Add a
host flag indicating that this host wishes to ignore ATA specific devices.

Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Cc: Victor Miasnikov <vvm@tut.by>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>