s390/ap: Implement SE bind and associate uevents

s390/ap: Implement SE bind and associate uevents

Notify userspace about two important events on AP queues
when run within Secure Execution (SE) environment:
- Send AP CHANGE uevent with "SE_BIND=1" on successful bind
  operation on this AP queue device.
- Send AP CHANGE uevent with "SE_ASSOC=<association_index>"
  on successful association operation with the secret of the
  reported index on this AP queue device.

Note there is no SE unbind/unassociate event. Unbind/unassociate
can have different triggers and technically there is no signaling
done which the AP code could catch. A user space application can,
if this information is crucial, query the sysfs attribute se_bind
on the AP queue which runs a synchronous TAPQ. If the attribute
returns with "unbound" a reset took place and SE bind and associate
states are unbound and unassociated.

Suggested-by: Marc Hartmayer mhartmay@linux.ibm.com
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>