s390/zcrypt: Show load of cards and queues in sysfs

Show the current load value of cards and queues in sysfs.
The load value for each card and queue is maintained by
the zcrypt device driver for dispatching and load
balancing requests over the available devices.

This patch provides the load value to userspace via a
new read only sysfs attribute 'load' per card and queue.

Signed-off-by: Harald Freudenberger <freude@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>