docs: fix trace docs build with sphinx 3.1.1

docs: fix trace docs build with sphinx 3.1.1

In Fedora 33 rawhide, we now have sphinx 3.1.1, as opposed
to previous 2.2.2. This new version generates a warning on
the source:

docs/qemu-option-trace.rst.inc:4:Malformed option description
  '[enable=]PATTERN', should look like "opt", "-opt args",
  "--opt args", "/opt args" or "+opt args"

This turns into an error when QEMU passes -W to sphinx-build

Strangely the previous 2.2.2 code has the exact same logic
for checking the syntax, but it is not being triggered. While
it is only complaining about the first option, I changed all
the options to give consistency.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200714162659.1017432-1-berrange@redhat.com>