s390/ap: Support AP card SCLP config and deconfig operations

Support SCLP AP adapter config and deconfig operations:
The sysfs deconfig attribute /sys/devices/ap/cardxx/deconfig
for each AP card is now read-write. Writing in a '1' triggers
a synchronous SCLP request to configure the adapter, writing
in a '0' sends a synchronous SCLP deconfigure request.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>