libata: Add a host flag to indicate lack of IORDY capability

This is the first preparation to doing the !IORDY cases properly.  Further
diffs will then add the needed logic to do it right.

Signed-off-by: Alan Cox <alan@redhat.com>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: Tejun Heo <htejun@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>