Pull up following revision(s) (requested by mrg in ticket #980):

sys/dev/usb/usbdivar.h: revision 1.117
sys/external/bsd/dwc2/dwc2.c: revision 1.52
sys/dev/usb/xhcivar.h: revision 1.10
sys/dev/usb/motg.c: revision 1.22
sys/dev/usb/ehci.c: revision 1.260
sys/dev/usb/ehci.c: revision 1.261
sys/dev/usb/xhci.c: revision 1.96
sys/dev/usb/ohci.c: revision 1.282
sys/dev/usb/ohci.c: revision 1.283
sys/dev/usb/ehcivar.h: revision 1.45
sys/dev/usb/uhci.c: revision 1.281
sys/dev/usb/uhci.c: revision 1.282
sys/dev/usb/usbdi.c: revision 1.177
sys/dev/usb/ohcivar.h: revision 1.60
sys/dev/usb/uhcivar.h: revision 1.55
(all via patch)

pull across abort fixes from nick-nhusb.  add more abort fixes, using
ideas from Taylor and Nick, and myself.  special thanks to both who
inspired much of the code here, if not wrote it directly.
among other problems, this assert should no longer trigger:

  panic: kernel diagnostic assertion "xfer->ux_state == XFER_ONQU" failed: file "/current/src/sys/dev/usb/usbdi.c", line 914

using usbhist i was able to track down my instance of it being related
to userland close() beginning, dropping the sc_lock, and then the usb
softintr completes the transfer normally, and when it is done, the
abort path attempts to re-complete the transfer, and the above assert
is tripped.

changes from nhusb were commited with these logs:
--
Move the struct usb_task to struct usbd_xfer for everyone to use.
--
Set device transfer status to USBD_IN_PROGRESS if start methods succeeds
--
Actually set the transfer status on transfers in ohci_abort_xfer and
the controller is dying
--
Don't supply the lock to callout_halt when polling as it won't be held
--
Improve transfer abort
--
Mark device transfers as USBD_IN_PROGRESS appropriately and improve
abort handling
--
--
Mark device transfers as USBD_IN_PROGRESS appropriately and improve
abort handling
--

additional changes include:
- initialise the usb abort task in the HCI allocx routine, so that it
  can be safely usb_rem_task()'d.
- rework the handling of softintr vs cancellation vs timeout abort based
  upon a scheme from Taylor:
  when completing a transfer normally:
  - if the status is not in progress, it must be cancelled or timed out,
    and we should not process this xfer.
  - set the status as normal.
  - unconditionallly callout_stop() and usb_rem_task().  they're safe and
    either aren't running, or will run and do nothing.
  - finally call usb_transfer_complete().
  when aborting a transfer:
  - status should be cancelled or timed out.
  - if cancelling, callout_halt and usb_rem_task_wait() to make sure the
    timer is either done or cancelled.
  - at this point, the ux_status must not be cancelled or timed out, and
    if it is not in progress we're done.
  - set the status.
  - if the controller is dying, just return.
  - perform HCI-specific tasks to abort this xfer.
  - finally call usb_transfer_complete().
  for the timeout and timeout task:
  - if the HCI is not dying, and the ux_status is in progress, then
    trigger the usb abort task.
- remove UXFER_ABORTWAIT and UXFER_ABORTING.

tested on:
- multiple PC systems with several types of devices: ugen/UPS, ucom,
  umass with disk, ssd and cdrom backends, kbd, ms, using uhci, ehci
  and xhci.
- erlite3: sd@umass on dwc2.
- sunblade2000: kbd/ms and umass disk on ohci.

untested:
- motg, slhci and ahci.  motg has some portion of the new scheme
  applied, but slhci and ahci require more study.

future work includes pushing a lot of the common abort handling into
usbdi.c and leaving upm_abort() for HC specific tasks, but this change
is pullup-able to netbsd-7 and netbsd-8 as it does not change any
external API, as well as removing over 100 lines of code while adding
over 30 new asserts.

XXX: pullup-7, pullup-8.

fix DIAGNOSTIC build by not copying ub_usepolling to stack before use

Sprinkle __diagused

(martin)