MFC r289563,r291481,r292537,r292538,r292542,r292543,r292544 and r292834:

MFC r289563,r291481,r292537,r292538,r292542,r292543,r292544 and r292834:

Update the LinuxKPI:
- Add more functions and types.
- Implement ACCESS_ONCE(), WRITE_ONCE() and READ_ONCE().
- Implement sleepable RCU mechanism using shared exclusive locks.
- Minor workqueue cleanup:
  - Make some functions global instead of inline to ease debugging.
  - Fix some minor style issues.
- In the zero delay case in queue_delayed_work() use the return value
  from taskqueue_enqueue() instead of reading "ta_pending" unlocked and
  also ensure the callout is stopped before proceeding.
- Implement drain_workqueue() function.
- Reduce memory consumption when allocating kobject strings in the
  LinuxKPI. Compute string length before allocating memory instead of
  using fixed size allocations. Make kobject_set_name_vargs() global
  instead of inline to save some bytes when compiling.

Sponsored by:	Mellanox Technologies

git-svn-id: svn://svn.freebsd.org/base/stable/10@293151 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f