acpi: pvpanic-isa: use AcpiDevAmlIfClass:build_dev_aml to provide device's AML

acpi: pvpanic-isa: use AcpiDevAmlIfClass:build_dev_aml to provide device's AML

.. and clean up not longer needed conditionals in DSTD build code
pvpanic-isa AML will be fetched and included when ISA bridge will
build its own AML code (including attached devices).

Expected AML change:
   the device under separate _SB.PCI0.ISA scope is moved directly
   under Device(ISA) node.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20220608135340.3304695-29-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>