selftests/mm: mseal, self_elf: factor out test macros and other duplicated items

Clean up and move some copy-pasted items into a new mseal_helpers.h.

1. The test macros can be made safer and simpler, by observing that
   they are invariably called when about to return.  This means that the
   macros do not need an intrusive label to goto; they can simply return.

2. PKEY* items.  We cannot, unfortunately use pkey-helpers.h.  The
   best we can do is to factor out these few items into mseal_helpers.h.

3. These tests still need their own definition of u64, so also move
   that to the header file.

4.  Be sure to include the new mseal_helpers.h in the Makefile
   dependencies.

[jhubbard@nvidia.com: include the new mseal_helpers.h in Makefile dependencies]
  Link: https://lkml.kernel.org/r/01685978-f6b1-4c24-8397-22cd3c24b91a@nvidia.com
Link: https://lkml.kernel.org/r/20240618022422.804305-3-jhubbard@nvidia.com


Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: Andrei Vagin <avagin@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rich Felker <dalias@libc.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>