Skip dnode handles use when not needed

Neither FreeBSD nor Linux currently implement kmem_cache_set_move(),
which means dnode_move() is never called. In such situation use of
dnode handles with respective locking to access dnode from dbuf is
a waste of time for no benefit.

This patch implements optional simplified code for such platforms,
saving at least 3 dnode lock/dereference/unlock per dbuf life cycle.
Originally I hoped to drop the handles completely to save memory,
but they are still used in dnodes allocation code, so left for now.

Before this change in CPU profiles of some workloads I saw 4-20% of
CPU time spent in zrl_add_impl()/zrl_remove(), which are gone now.

Reviewed-by: Rob Wing <rob.wing@klarasystems.com
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Allan Jude <allan@klarasystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.
Closes #16374