qapi: Fix indentation, again

qapi: Fix indentation, again

In commit 26ec4e53f2 and similar commits we fixed the indentation
for doc comments in our qapi json files to follow a new stricter
standard for indentation, which permits only:
    @arg: description line 1
          description line 2

or:
    @arg:
    line 1
    line 2

Unfortunately since we didn't manage to get the script changes that
enforced the new style in, a variety of commits (eg df4097aeaf71,
2e4457032105) introduced new doc text which doesn't follow the new
stricter rules for indentation on multi-line doc comments.  Bring
those into line with the new rules.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20200810195019.25427-3-peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>