Convert vm_page_alloc() callers to use vm_page_alloc_noobj().

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
Sponsored by: The FreeBSD Foundation

(cherry picked from commit a4667e09e6520dc2c4b0b988051f060fed695a91)