OvmfPkg: resolve PciSegmentLib

OvmfPkg: resolve PciSegmentLib

In the next patch we'll build "MdeModulePkg/Bus/Pci/PciHostBridgeDxe".
That driver depends on the PciSegmentLib class. Edk2 offers four
instances:

(1) MdePkg/Library/UefiPciSegmentLibPciRootBridgeIo/

    Inappropriate here because it consumes
    EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL, but
    "MdeModulePkg/Bus/Pci/PciHostBridgeDxe" needs the library class for
    producing that protocol.

(2) MdePkg/Library/PeiPciSegmentLibPciCfg2/

    Restricted to PEIM, SEC, and PEI_CORE client modules.

(3) MdePkg/Library/DxePciSegmentLibEsal/

    "uses ESAL services to perform PCI Configuration cycles"

(4) MdePkg/Library/BasePciSegmentLibPci/

    A simple BASE library instance that sits on top of PciLib. This is our
    choice. We can resolve PciSegmentLib to this instance for all module
    types.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>