selftests: soft-dirty: add test for mprotect

Add two soft-dirty test cases for mprotect() on both anon or file.

Link: https://lkml.kernel.org/r/20220725142048.30450-3-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>