Merge patch series "fs: last of the pseudofs mount api conversions"

Eric Sandeen <sandeen@redhat.com> says:

pstore used mount_single, which used to transparently do a
remount operation on a fresh mount of an existing superblock.
The new get_tree_single does not do this, but prior discussion
on fsdevel seems to indicate that this isn't expected to be a
problem. We can watch for issues.

devpts is just a forward port from work dhowells did already, and it
seems straightforward. I left error messages as they are rather than
converting to the mount API message channel for now.

devtmpfs was already converted, but left a .mount in place, rather
than using .get_tree. The solution to this is ... unique so some
scrutiny is probably wise.

The last patch removes reconfigure_single, mount_single, and
compare_single because no users remain, but we could also wait until
all conversions are done, and remove all infrastructure at that time
instead, if desired.

* patches from https://lore.kernel.org/r/20250205213931.74614-1-sandeen@redhat.com:
  vfs: remove some unused old mount api code
  devtmpfs: replace ->mount with ->get_tree in public instance
  vfs: Convert devpts to use the new mount API
  pstore: convert to the new mount API

Link: https://lore.kernel.org/r/20250205213931.74614-1-sandeen@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>