s390/cio: Export information about Endpoint-Security Capability

Add a new sysfs attribute 'esc' per chpid. This new attribute exports
the Endpoint-Security-Capability byte of channel-path description block,
which could be 0-None, 1-Authentication, 2 and 3-Encryption.

For example:
$ cat /sys/devices/css0/chp0.34/esc
0

[vneethv@linux.ibm.com: cleaned-up & modified description]

Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>