vm_page: Consolidate page busy sleep mechanisms

vm_page: Consolidate page busy sleep mechanisms

- Modify vm_page_busy_sleep() and vm_page_busy_sleep_unlocked() to take
  a VM_ALLOC_* flag indicating whether to sleep on shared-busy, and fix
  up callers.
- Modify vm_page_busy_sleep() to return a status indicating whether the
  object lock was dropped, and fix up callers.
- Convert callers of vm_page_sleep_if_busy() to use vm_page_busy_sleep()
  instead.
- Remove vm_page_sleep_if_(x)busy().

No functional change intended.

Obtained from:	jeff (object_concurrency patches)
Reviewed by:	kib

(cherry picked from commit 87b646630c4892e21446cd096bea6bcaecea33ac)