docs/devel/loads-stores: Fix git grep regexes

docs/devel/loads-stores: Fix git grep regexes

The loads-and-stores documentation includes git grep regexes to find
occurrences of the various functions.  Some of these regexes have
errors, typically failing to escape the '?', '(' and ')' when they
should be metacharacters (since these are POSIX basic REs). We also
weren't consistent about whether to have a ':' on the end of the
line introducing the list of regexes in each section.

Fix the errors.

The following shell rune will complain about any REs in the
file which don't have any matches in the codebase:
 for re in $(sed -ne 's/ - ``\(\\<.*\)``/\1/p' docs/devel/loads-stores.rst); do git grep -q "$re" || echo "no matches for re $re"; done

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20230904161703.3996734-1-peter.maydell@linaro.org