KVM: s390: adapter interrupt sources

Add a new interface to register/deregister sources of adapter interrupts
identified by an unique id via the flic. Adapters may also be maskable
and carry a list of pinned pages.

These adapters will be used by irq routing later.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>