cifs: add missing debug entries for kconfig options

/proc/fs/cifs/DebugData displays the features (Kconfig options)
used to build cifs.ko but it was missing some, and needed comma
separator.  These can be useful in debugging certain problems
so we know which optional features were enabled in the user's build.
Also clarify them, by making them more closely match the
corresponding CONFIG_CIFS_* parm.

Old format:
Features: dfs fscache posix spnego xattr acl

New format:
Features: DFS,FSCACHE,SMB_DIRECT,STATS,DEBUG2,ALLOW_INSECURE_LEGACY,CIFS_POSIX,UPCALL(SPNEGO),XATTR,ACL

Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Reviewed-by: Paulo Alcantara <palcantara@suse.de>
CC: Stable <stable@vger.kernel.org>