cifs: move cache mount options to fs_context.ch

Helps to shrink connect.c and make it more readable
by moving mount related code to fs_context.c and
fs_context.h

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>