x86: pci: acpi: consolidate PCI slots creation

x86: pci: acpi: consolidate PCI slots creation

No functional changes nor AML bytecode changes.
Consolidate code that generates empty and populated slot
descriptors. Besides eliminating duplication,
it helps consolidate conditions for generating
parts of Device{} desriptor in one place, which makes
code more compact and easier to read.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20220701133515.137890-18-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>