* Add ->host_busy field to struct ide_host and use it's first bit
together with lock bitops to provide new ports serialization method.
* Convert core IDE code to use new ide_[un]lock_host() helpers.
This removes the need for taking hwgroup->lock if host is already
busy on serialized hosts and makes it possible to merge ide_hwgroup_t
into ide_hwif_t (done in the later patch).
* Remove no longer needed ide_hwgroup_t.busy and ide_[un]lock_hwgroup().
* Update do_ide_request() documentation.
v2:
* ide_release_lock() should be called inside IDE_HFLAG_SERIALIZE check.
* Add ide_hwif_t.busy flag and ide_[un]lock_port() for serializing
devices on a port.
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>