acpi: refactor pxb crs computation

Instead of always passing both IO and MEM ranges when
computing CRS ranges, define a new CrsRangeSet structure
that include them both.

This is done before introducing a third type of range,
64-bit MEM, so it will be easier to pass them all around.

Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>