KVM: PPC: Book3S HV: XIVE: Add a mapping for the source ESB pages

Each source is associated with an Event State Buffer (ESB) with a
even/odd pair of pages which provides commands to manage the source:
to trigger, to EOI, to turn off the source for instance.

The custom VM fault handler will deduce the guest IRQ number from the
offset of the fault, and the ESB page of the associated XIVE interrupt
will be inserted into the VMA using the internal structure caching
information on the interrupts.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

Documentation/virtual/kvm/devices/xive.txt

@@ -36,6 +36,13 @@ the legacy interrupt mode, referred as XICS (POWER7/8).
   third (operating system) and the fourth (user level) are exposed the
   guest.
 
+  2. Event State Buffer (ESB)
+
+  Each source is associated with an Event State Buffer (ESB) with
+  either a pair of even/odd pair of pages which provides commands to
+  manage the source: to trigger, to EOI, to turn off the source for
+  instance.
+
 * Groups:
 
   1. KVM_DEV_XIVE_GRP_CTRL