memory: Split mtree_info() as mtree_info_flatview() + mtree_info_as()

memory: Split mtree_info() as mtree_info_flatview() + mtree_info_as()

While mtree_info() handles both ASes and flatviews cases,
the two cases share basically no code. Split mtree_info()
as mtree_info_flatview() + mtree_info_as() to simplify.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210904231101.1071929-2-philmd@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>