pcihp: do not put empty PCNT in DSDT

pcihp: do not put empty PCNT in DSDT

count number of PCNT methods that actually call Notify
and if there aren't any, drop PCNT altogether.
It mostly affects 'Q35' tests where there is no root-ports
/bridges attached and 'PC' machine when ACPI PCI hotplug is
completely disabled.

Expected ASL change:

-            Method (PCNT, 0, NotSerialized)
-            {
-            }
...
         Method (_E01, 0, NotSerialized)  // _Exx: Edge-Triggered GPE
         {
-            Acquire (\_SB.PCI0.BLCK, 0xFFFF)
-            \_SB.PCI0.PCNT ()
-            Release (\_SB.PCI0.BLCK)
         }

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20230112140312.3096331-23-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>