selftests/mm: add process_madvise() tests

selftests/mm: add process_madvise() tests

Add tests for process_madvise(), focusing on verifying behavior under
various conditions including valid usage and error cases.

[lianux.mm@gmail.com: v7]
Link: https://lkml.kernel.org/r/20250729113109.12272-1-lianux.mm@gmail.com
Link: https://lkml.kernel.org/r/20250729113109.12272-1-lianux.mm@gmail.com
Link: https://lkml.kernel.org/r/20250721114614.40996-1-lianux.mm@gmail.com
Signed-off-by: wang lian <lianux.mm@gmail.com>
Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Suggested-by: Zi Yan <ziy@nvidia.com>
Suggested-by: Mark Brown <broonie@kernel.org>
Acked-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Tested-by: Zi Yan <ziy@nvidia.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>