ArmVirtPkg/FdtPciHostBridgeLib: Add extra pci root buses support

ArmVirtPkg/FdtPciHostBridgeLib: Add extra pci root buses support

In order to take advantages of extra pci root buses in ArmVirtPkg, it is
necessary to scan extra root buses when getting root briges. And now
PciHostBridgeUtilityLib already provides a set of utility functions that
support for extra pci root buses, like PciHostBridgeUtilityGetRootBridges()
/ PciHostBridgeUtilityFreeRootBridges(). So let's rebase
ArmVirtPkg/FdtPciHostBridgeLib to PciHostBridgeUtilityGetRootBridges() /
PciHostBridgeUtilityFreeRootBridges() to extend ArmVirtPkg with extra
pci root buses support.

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3059

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Signed-off-by: Jiahui Cen <cenjiahui@huawei.com>
Signed-off-by: Yubo Miao <miaoyubo@huawei.com>
Message-Id: <20210119011302.10908-11-cenjiahui@huawei.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>