selftests/mm: fix vm_util.c build failures: add snapshot of fs.h

On Ubuntu 23.04, on a clean git tree, the selftests/mm build fails due 10
or 20 missing items, all of which are found in fs.h, which is created via
"make headers".  However, as per [1], the idea is to stop requiring "make
headers", and instead, take a snapshot of the files and check them in.

Here are a few of the build errors:

vm_util.c:34:21: error: variable has incomplete type 'struct pm_scan_arg'
        struct pm_scan_arg arg;
...
vm_util.c:45:28: error: use of undeclared identifier 'PAGE_IS_WPALLOWED'
...
vm_util.c:55:21: error: variable has incomplete type 'struct page_region'
...
vm_util.c:105:20: error: use of undeclared identifier 'PAGE_IS_SOFT_DIRTY'

To fix this, add fs.h, taken from a snapshot of ./usr/include/linux/fs.h
after running "make headers".

[1] commit e076eaca ("selftests: break the dependency upon local
header files")

Link: https://lkml.kernel.org/r/20240618022422.804305-5-jhubbard@nvidia.comSigned-off-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrei Vagin <avagin@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jeff Xu <jeffxu@chromium.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>