docs: filesystems: vfs: actualize struct super_operations description

Added/updated descriptions for super_operations:
- free_inode method
- evict_inode method
- freeze_super/thaw_super method
- show_{devname,path,stats} procfs-related methods
- get_dquots method

Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20230313130718.253708-3-aleksandr.mikhalitsyn@canonical.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>