ArmVirtPkg/FdtPciHostBridgeLib: map ECAM and I/O spaces in GCD memory map

Up until now, we have been getting away with not declaring the ECAM
and translated I/O spaces at all in the GCD memory map, simply because
we map the entire address space with device attributes in the early PEI
code, and so the ECAM space will be mapped wherever it ends up.

Now that we are about to make changes to how ArmVirtQemu reasons
about the size of the address space, it would be better to get rid
of this mapping of the entire address space, since it can get
arbitrarily large without real benefit.

So start by mapping the ECAM and translated I/O spaces explicitly,
instead of relying on the early PEI mapping.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>