qemu-options.hx: Fix up the autogenerated rST

This commit contains hand-written fixes for some issues with the
autogenerated rST fragments in qemu-options.hx:

 * Sphinx complains about the UTF-8 art table in the documentation of
   the -drive option.  Replace it with a proper rST format table.

 * rST does not like definition list entries with no actual
   definition, but it is possible to work around this by putting a
   single escaped literal space as the definition line.

 * The "-g widthxheight" option documentation suffers particularly
   badly from losing the distinction between italics and fixed-width
   as a result of the auto conversion, so put it back in again.

 * The script missed some places that use the |qemu_system| etc
   macros and need to be marked up as parsed-literal blocks.

 * The script autogenerated an expanded out version of the
   contents of qemu-option-trace.texi; replace it with an
   qemu-option-trace.rst.inc include.

This is sufficient that we can enable inclusion of the
option documentation from invocation.rst.

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: 20200228153619.9906-28-peter.maydell@linaro.org