hw/pci-host/gpex-acpi: Add support for dsdt construction for pxb-cxl

hw/pci-host/gpex-acpi: Add support for dsdt construction for pxb-cxl

This adds code to instantiate the slightly extended ACPI root port
description in DSDT as per the CXL 2.0 specification.

Basically a cut and paste job from the i386/pc code.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220429144110.25167-30-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>