sphinx: qapidoc: Wrap "If" section body in a paragraph node

sphinx: qapidoc: Wrap "If" section body in a paragraph node

These sections need to be wrapped in a block-level element, such as
Paragraph in order for them to be rendered into Texinfo correctly.

Before (e.g.):

<section ids="qapidoc-713">
  <title>If</title>
  <literal>defined(CONFIG_REPLICATION)</literal>
</section>

became:

  .SS If
  \fBdefined(CONFIG_REPLICATION)\fP.SS \fBBlockdevOptionsReplication\fP (Object)
  ...

After:

<section ids="qapidoc-713">
  <title>If</title>
  <paragraph>
    <literal>defined(CONFIG_REPLICATION)</literal>
  </paragraph>
</section>

becomes:

  .SS If
  .sp
  \fBdefined(CONFIG_REPLICATION)\fP
  .SS \fBBlockdevOptionsReplication\fP (Object)
  ...

Reported-by: Markus Armbruster <armbru@redhat.com>
Tested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20210406141909.1992225-2-jsnow@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>