Cherry-pick from FreeBSD SVN:
Subject: svn commit: r258399 - head/sys/crypto/aesni

Author: jmg
Date: Wed Nov 20 20:25:27 2013
New Revision: 258399
URL: http://svnweb.freebsd.org/changeset/base/258399

Log:
 flag that the aesni driver is sync...  This means we don't waste a
 context switch just to call the done callback...  On my machine, this
 improves geli/gzero decrypt performance by ~27% from 550MB/sec to
 ~700MB/sec...
Disable a few debugging printf's in zvol.c.  These messages should
be output by userland applications anyways.

The underlying problem is that we are using different way of making
minor numbers for device nodes, and the current construction is not
quite working right and needs restructuring.

Ticket: #3263