libacpi: report PCI slots as enabled only for hotpluggable devices

DSDT for qemu-xen lacks _STA method of PCI slot object. If _STA method
doesn't exist then the slot is assumed to be always present and active
which in conjunction with _EJ0 method makes every device ejectable for
an OS even if it's not the case.

qemu-kvm is able to dynamically add _EJ0 method only to those slots
that either have hotpluggable devices or free for PCI passthrough.
As Xen lacks this capability we cannot use their way.

qemu-xen-traditional DSDT has _STA method which only reports that
the slot is present if there is a PCI devices hotplugged there.
This is done through querying of its PCI hotplug controller.
qemu-xen has similar capability that reports if device is "hotpluggable
or absent" which we can use to achieve the same result.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

tools/libacpi/mk_dsdt.c

@@ -439,9 +439,10 @@ int main(int argc, char **argv)
             pop_block();
         }
     } else {
-        stmt("OperationRegion", "SEJ, SystemIO, 0xae08, 0x04");
+        stmt("OperationRegion", "SEJ, SystemIO, 0xae08, 0x08");
         push_block("Field", "SEJ, DWordAcc, NoLock, WriteAsZeros");
         indent(); printf("B0EJ, 32,\n");
+        indent(); printf("B0RM, 32,\n");
         pop_block();
 
         /* hotplug_slot */
@@ -452,6 +453,12 @@ int main(int argc, char **argv)
                     stmt("Store", "%#010x, B0EJ", 1 << slot);
                 } pop_block();
                 stmt("Name", "_SUN, %i", slot);
+                push_block("Method", "_STA, 0"); {
+                    push_block("If", "And(B0RM, ShiftLeft(1, %i))", slot);
+                    stmt("Return", "0xF");
+                    pop_block();
+                    stmt("Return", "0x0");
+                } pop_block();
             } pop_block();
         }
     }