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
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D32947