vm: stop trylocking page queues in vm_page_pqbatch_submit

About 11 minutes of poudriere -s -j 104 and probing on return value of
trylocks reveals that over 10% of attempts fail, which in turn means
there are more atomics performed than necessary.

Trylocking was there to try preventing migration, but it's not very likely
to happen if the lock is uncontested.

Reviewed by: markj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D21925