VT-d/qinval: eliminate redundant locking

VT-d/qinval: eliminate redundant locking

The qinval-specific lock would only ever get used with the IOMMU's
register lock already held. Along with dropping the lock also drop
another unused field from struct qi_ctrl.

Furthermore the gen_*_dsc() helpers become pretty pointless with the
lock dropped - being each used only in a single place, simply fold
them into their callers.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>