MFC r250395 (by attilio / jeff):
Generalize the bitset operations, present in cpuset and offer a KPI to
redefine such operations for different consumers.
This will be used when NUMA support will be finished and numaset
will need to be used.
MFC r251703 (by attilio):
 - Add a BIT_FFS() macro and use it to replace cpusetffs_obj()
MFC r255363:
Micro-optimize cpu_search(), allowing compiler to use more efficient inline
ffsl() implementation, when it is available, instead of homegrown iteration.

On dual-E5645 amd64 system (2x6x2 cores) under heavy I/O load that reduces
time spent inside cpu_search() from 19% to 13%, while IOPS increased by 5%.
MFC r249102 (by trasz):
Since the CTL version in FreeBSD does not support High Availability,
ctl_is_single should always be set to 1.  Make it so.  Previously
it was always 0, because ctl_isc_start() never got to run.
MFC r249256 (by ken):
Fix a memory leak that showed up when we delete LUNs.  The memory used for
the LUN was never freed.

ctl.c:          Adjust ctl_alloc_lun() to make sure we don't clear the
                CTL_LUN_MALLOCED flag.
MFC r249438:
Use full freeze while PMP does hard reset. This is only cosmetical change.
MFC r249466, r249481, r250025:
Remove multilevel freezing mechanism, implemented to handle specifics of
the ATA/SATA error recovery, when post-reset recovery commands should be
allocated when queues are already full of payload requests.  Instead of
removing frozen CCBs with specified range of priorities from the queue
to provide free openings, use simple hack, allowing explicit CCBs over-
allocation for requests with priority higher (numerically lower) then
CAM_PRIORITY_OOB threshold.

Simplify CCB allocation logic by removing SIM-level allocation queue.
After that SIM-level queue manages only CCBs execution, while allocation
logic is localized within each single device.