Remove page zeroing code from consumers and stop specifying
VM_ALLOC_NOOBJ.  In a few places, also convert an allocation loop to
simply use VM_ALLOC_WAITOK.

Similarly, convert vm_page_alloc_domain() callers.

Note that callers are now responsible for assigning the pindex.

Reviewed by:	alc, hselasky, kib
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D31986