bhyve.8: Correct description for -c flag, tag spdx

The examples only show the usage of `-c <numcpus>`, as did the flag
description, however the -c flag supports more complex cpu topology
specifiers. These were documented correctly in SYNOPSIS, add them to
the body of the DESCRIPTION as well. Someone could go further and do
and example with using them.

MFC after:	3 days
Event:		OpenZFS Developer Summit '25
Reported by:	Levi Worley <levi@gainframe.com>

usr.sbin/bhyve/bhyve.8

@@ -1,3 +1,6 @@
+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
 .\" Copyright (c) 2013 Peter Grehan
 .\" All rights reserved.
 .\"
@@ -22,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd September 16, 2025
+.Dd October 28, 2025
 .Dt BHYVE 8
 .Os
 .Sh NAME
@@ -125,7 +128,7 @@ xAPIC mode is the default setting so this option is redundant.
 It will be deprecated in a future version.
 .It Fl C
 Include guest memory in core files.
-.It Fl c Op Ar setting ...
+.It Fl c Oo Oo Cm cpus= Oc Ns Ar numcpus Oc Ns Oo Cm ,sockets= Ns Ar n Oc Ns Oo Cm ,cores= Ns Ar n Oc Ns Oo Cm ,threads= Ns Ar n Oc
 Number of guest virtual CPUs
 and/or the CPU topology.
 The default value for each of