selftests/mm: use TEST_GEN_PROGS where proper

TEST_GEN_PROGS and TEST_GEN_FILES are used randomly in the mm/Makefile to
specify programs that need to build.  Logically all these binaries should
all fall into TEST_GEN_PROGS.

Replace those TEST_GEN_FILES with TEST_GEN_PROGS, so that we can reference
all the tests easily later.

[peterx@redhat.com: tools/testing/selftests/mm/Makefile: don't wipe out TEST_GEN_PROGS]
  Link: https://lkml.kernel.org/r/ZDxrvZh/cw357D8P@x1n
Link: https://lkml.kernel.org/r/20230412164218.328104-1-peterx@redhat.com


Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>