[S390] dasd: no High Performance FICON in 31-bit mode

The High Performance FICON feature is not supported in 31-bit mode,
no matter what the various flags say. So we need to check for the
CONFIG_64BIT option as well.

Signed-off-by: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>