s390: connector support

Include connector config in the s390 arch Kconfig to get support for
connectors.

This also fixes the following Kconfig warning:
fs/Kconfig:1728:warning: 'select' used by config symbol 'CIFS_UPCALL' refer to undefined symbol 'CONNECTOR'

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>