MdeModulePkg/PciHostBridgeLib: Add ResourceAssigned field

MdeModulePkg/PciHostBridgeLib: Add ResourceAssigned field

Some platform doesn't require PciBus driver to assign resource
to PCI devices which causes PciRootBridgeIo.Configuration() cannot
return correct resource information to caller.

When resource assignment by PciBus is not mandatory, only light
version of PCI bus enumeration is performed, which only collects
the device resource consumption and publishes the PciIo instance.
The corresponding logic is in PciEnumeratorLight() in PciBus driver.

But PciEnumeratorLight() still depends on
PciRootBridgeIo.Configuration() returns the starting bus number in
order to search down to find all PCI devices under the root bridge.

When ResourceAssigned in PCI_ROOT_BRIDGE returned by
PciHostBridgeGetRootBridges() is TRUE, PciHostBridge driver treats
the Bus/Io/Mem/MemAbove4G/PMem/PMemAbove4G as the resource that are
*actually assigned* to the root bridge, instead of the resource that
*can be assigned* to the root bridge.
So that PciRootBridgeIo.Configuration() can return the correct
information.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>