cifs: make fs_context error logging wrapper

This new helper will be used in the fs_context mount option parsing
code. It log errors both in:
* the fs_context log queue for userspace to read
* kernel printk buffer (dmesg, old behaviour)

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>