ArmVirtualizationPkg/PciHostBridgeDxe: abort if there's no PCI host bridge

ArmVirtualizationPkg/PciHostBridgeDxe: abort if there's no PCI host bridge

If VirtFdtDxe found no PCI host in the DTB, then the config space base
address will be left at zero -- the default is set in the DSC --, and we
should exit PciHostBridgeDxe immediately.

This causes gEfiPciRootBridgeIoProtocolGuid not to be installed, which in
turn prevents MdeModulePkg/Bus/Pci/PciBusDxe from binding (see
PciBusDriverBindingSupported()).

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Olivier Martin <Olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16898 6f19259b-4bc3-4df7-8a09-765794883524