Ovmf/PlatformPei: Use host-provided GPA end if available

Read the "hardware-info" item from fw-cfg to extract specifications
of PCI host bridges and analyze the 64-bit apertures of them to
find out the highest 64-bit MMIO address required which determines
the address space required by the guest, and, consequently, the
FirstNonAddress used to calculate size of physical addresses.

Using the static PeiHardwareInfoLib, read the fw-cfg file of
hardware information to extract, one by one, all the host
bridges. Find the last 64-bit MMIO address of each host bridge,
using the HardwareInfoPciHostBridgeLib API, and compare it to an
accumulate value to discover the highest address used, which
corresponds to the highest value that must be included in the
guest's physical address space.

Given that platforms with multiple host bridges may provide the PCI
apertures' addresses, the memory detection logic must take into
account that, if the host provided the MMIO windows that can and must
be used, the guest needs to take those values. Therefore, if the
MMIO windows are found in the host-provided fw-cfg file, skip all the
logic calculating the physical address size and just use the value
provided. Since each PCI host bridge corresponds to an element in
the information provided by the host, each of these must be analyzed
looking for the highest address used.

Cc: Alexander Graf <graf@amazon.de>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Nicolas Ojeda Leon <ncoleon@amazon.com>

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