smb: client: introduce cifs_sfu_make_node()

[ Upstream commit b0348e45 ]

Remove duplicate code and add new helper for creating special files in
SFU (Services for UNIX) format that can be shared by SMB1+ code.

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>