Convert VirtIO to use ithreads instead of taskqueues

Contains projects/virtio commits:

r245709:
    Each VirtIO device was scheduling its own taskqueue(9) to do the
    off-level interrupt handling. ithreads(9) is the more nature way
    to do this. The primary motivation for this work to better support
    network multiqueue.
r245710:
    virtio: Change virtqueue intr handlers to return void
r245711:
    virtio_blk: Remove interrupt taskqueue
r245721:
    vtnet: Remove interrupt taskqueue
r245722:
    virtio_scsi: Remove interrupt taskqueue
r245747:
    vtnet: Remove taskqueue fields missed in r245721

MFC after:	1 month
Merge several virtio_blk changes from projects/virtio

The notable changes of this commit are support for disk resizing
and chases updates to the spec regarding write caching.

Contains projects/virtio commits:

r245713:
    virtio_blk: Replace __FUNCTION__ with __func__
r245714:
    virtio_blk: Use more consistent mutex name
r245715:
    virtio_blk: Print device name too if failed to reinit during dump
r245716:
    virtio_blk: Remove an unuseful ASSERT
r245723:
    virtio_blk: Record the vendor and device information
r245724:
    virtio_blk: Add resize support
r245726:
    virtio_blk: More verbose ASSERT messages
r245730:
    virtio_blk: Tweak resize announcement message
r246061:
    virtio_blk: Do not always read entire config
r246062:
    virtio_blk: Use topology to set the stripe size/offset
r246307:
    virtio_blk: Correct stripe offset calculation
r246063:
    virtio_blk: Add support for write cache enable feature
r246303:
    virtio_blk: Expand a comment
r252529:
    virtio_blk: Improve write cache handling
r252681:
    virtio_blk: Remove unneeded curly braces

MFC after:	1 month
Merge virtio_balloon changes from projects/virtio

Contains projects/virtio commits:

r245717:
    virtio_balloon: Make the softc lock a regular mutex
r245718:
    virtio_balloon: Remove two unuseful ASSERTs
r245719:
    virtio_balloon: More verbose ASSERT messages
r245720:
    virtio_balloon: Simplify lowmem handling in vtballoon_inflate()
r252530:
    virtio_balloon: Use just a kthread instead of dedciated kproc
r252568:
    virtio_balloon: Need to use kthread_exit() after r252530

MFC after:	1 month
- Read all TP parameters in one place.
- Read the filter mode, calculate various shifts, and use them
  properly during active open (in select_ntuple).

MFC after:	1 day
Merge vtnet changes from projects/virtio

Minor changes to the network driver. A multiqueue driver that is
a significant rewrite will be in merged shortly.

Contains projects/virtio commits:

r246058:
    vtnet: Move an mbuf ASSERT to the calling function
r246059:
    vtnet: Tweak ASSERT message

MFC after:	1 month
Merge virtio changes from projects/virtio

Contains projects/virtio commits:

r245738:
    virtio: Minor man page tweaks
r246060:
    virtio: Cleanup feature description printing
r246306:
    virtio: Remove old debugging flag
r247238:
    virtio: Remove PRIx64 macros from format strings
r247239:
    virtio: Constify some fields
r247240:
    virtio: Minor code simplifications
r249962:
    virtio: Update to my freebsd.org email address

MFC after:	1 month
Merge virtio_pci changes from projects/virtio

This commit is primarily a significant cleanup to the interrupt
allocation code that had gotten a bit jumbled from having to
support per-vq MSIX, shared MSIX, MSI, and legacy style interrupts.

Contains projects/virtio commits:

r246064:
    virtio_pci: Rewrite allocation of interrupts
r246065:
    virtio_pci: Remove spaces before a tab
r246066:
    virtio_pci: Dynamically allocate the virtqueue array
r246304:
    virtio_pci: Clean up after failed virtqueue alloc attempt
r246305:
    virtio_pci: Move no interrupt check into the PCI interrupt handlers
r246308:
    virtio_pci: Remove unused variable

MFC after:	1 month
Merge virtio_scsi change from projects/virtio

r252680:
    Fix SIM lock not owned panic

    The CAM locking requirements of registering an async
    callback has changed so the SIM lock must be held. Remove
    code that explicitly dropped the lock around the register.

    Also return CAM_SEL_TIMEOUT instead of CAM_TID_INVALID
    for bad targets to avoid a lot console spam during bus
    scans.

MFC after:	1 month