DynamicTablesPkg: AcpiSsdtPcieLibArm : Add UID to slot creation

DynamicTablesPkg: AcpiSsdtPcieLibArm : Add UID to slot creation

Expose the UID value to GeneratePciSlots().
This is needed for some cases for example:
https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#identifying-externally-exposed-pcie-root-ports

Name (_DSD, Package () {
  ToUUID("EFCC06CC-73AC-4BC3-BFF0-76143807C389"),
  Package () {
    Package (2) {"ExternalFacingPort", 1},
    Package (2) {"UID", 0},
  }
})

Signed-off-by: Jeff Brasen <jbrasen@nvidia.com>
Reviewed-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>