scripts/qemu-trace-stap: Convert documentation to rST

scripts/qemu-trace-stap: Convert documentation to rST

The qemu-trace-stap documentation is currently in
scripts/qemu-trace-stap.texi in Texinfo format, which we
present to the user as:
 * a qemu-trace-stap manpage
 * but not (unusually for QEMU) part of the HTML docs

Convert the documentation to rST format that lives in
the docs/ subdirectory, and present it to the user as:
 * a qemu-trace-stap manpage
 * part of the interop/ Sphinx manual

There are minor formatting changes to suit Sphinx, but no
content changes.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20200124162606.8787-8-peter.maydell@linaro.org