pcihp: acpi: decouple hotplug and generic slots description

pcihp: acpi: decouple hotplug and generic slots description

Split build_append_pci_bus_devices() onto generic part that builds
AML descriptions only for populated slots which is applicable to
both hotplug disabled and enabled bridges. And a hotplug only
part that complements generic AML with hotplug depended bits
(that depend on BSEL), like _SUN/_EJ0 entries, dynamic _DSM.

Hotplug part, will generate full 'Device' descriptors for
non-populated slots (like it used to be) and complementary
'Scope' descriptors for populated slots that are hotplug capable.
i.e. something like this:
  - ...
  +                Name (BSEL, 0x03)
  +                Scope (S00)
  +                {
  +                    Name (ASUN, Zero)
  +                    Method (_DSM, 4, Serialized)  // _DSM: Device-Specific Method
  +                    {
  +                        Local0 = Package (0x02)
  +                            {
  +                                BSEL,
  +                                ASUN
  +                            }
  +                        Return (PDSM (Arg0, Arg1, Arg2, Arg3, Local0))
  +                    }
  +  [ ... other hotplug depended bits ]
  +                }

While generic build_append_pci_bus_devices() still calls hotplug part at
its end it doesn't really depend on any hotplug bits anymore and later
both could be completely separated when it's necessary.

Main benefit though is that both build_append_pci_bus_devices() and
build_append_pcihp_slots() become more readable and it makes easier
to modify them with less risk of affecting another part. Also it opens
possibility to re-use generic part elsewhere (microvm, arm/virt).

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20230112140312.3096331-34-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>