OvmfPkg/IndustryStandard: define PCI Capabilities for QEMU's PCI Bridges

OvmfPkg/IndustryStandard: define PCI Capabilities for QEMU's PCI Bridges

QEMU has recently gained the ability to provide various hints about its
PCI bridges. The hints take the form of vendor-specific PCI capabilities.
Define macros and types under "OvmfPkg/Include/IndustryStandard" to
describe these capabilities.

The definitions correspond to "docs/pcie_pci_bridge.txt" in the QEMU tree.
Said documentation was added in the last commit of the following series:

  a35fe226558a hw/pci: introduce pcie-pci-bridge device
  70e1ee59bb94 hw/pci: introduce bridge-only vendor-specific capability to
               provide some hints to firmware
  226263fb5cda hw/pci: add QEMU-specific PCI capability to the Generic PCI
               Express Root Port
  c1800a162765 docs: update documentation considering PCIE-PCI bridge

We are going to parse the Resource Reservation Capability in
OvmfPkg/PciHotPlugInitDxe, and return the reservation requests to
PciBusDxe.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>