BACKPORT: selftests/mm: add uffd_test_case_ops to allow test case-specific operations

Currently each test can specify unique operations using uffd_test_ops,
however these operations are per-memory type and not per-test.  Add
uffd_test_case_ops which each test case can customize for its own needs
regardless of the memory type being used.  Pre- and post-allocation
operations are added, some of which will be used in the next patch to
implement test-specific operations like madvise after memory is allocated
but before it is accessed.

Link: https://lkml.kernel.org/r/20231206103702.3873743-5-surenb@google.com


Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: ZhangPeng <zhangpeng362@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

(cherry picked from commit e8a42240)
Conflicts:
	tools/testing/selftests/mm/uffd-common.c
	tools/testing/selftests/mm/uffd-common.h
	tools/testing/selftests/mm/uffd-unit-tests.c
	tools/testing/selftests/vm/userfaultfd.c

1. Userfaultfd selftest was split into separate uffd-* files and moved
   to selftests/mm.
2. In 6.1 there is no mechanism to run individual unit-tests. All
   unit-tests are run after stress test. Consequently, the tests are not
   abstracted using 'uffd_test_case_t'. Therefore, added
   'uffd_test_case_ops' as a parameter to uffd_test_ctx_init().

Bug: 274911254
Change-Id: I6480abf1709ca717d9baad5047bf675852f10726
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>