OvmfPkg/AcpiPlatformDxe: alloc blobs from 64-bit space unless restricted

OvmfPkg/AcpiPlatformDxe: alloc blobs from 64-bit space unless restricted

... by narrower than 8-byte ADD_POINTER references.

Introduce the CollectAllocationsRestrictedTo32Bit() function, which
iterates over the linker/loader script, and collects the names of the
fw_cfg blobs that are referenced by QEMU_LOADER_ADD_POINTER.PointeeFile
fields, such that QEMU_LOADER_ADD_POINTER.PointerSize is less than 8. This
means that the pointee blob's address will have to be patched into a
narrower-than-8 byte pointer field, hence the pointee blob must not be
allocated from 64-bit address space.

In ProcessCmdAllocate(), consult these restrictions when setting the
maximum address for gBS->AllocatePages(). The default is now MAX_UINT64,
unless restricted like described above to the pre-patch MAX_UINT32 limit.

In combination with Ard's QEMU commit cb51ac2ffe36 ("hw/arm/virt: generate
64-bit addressable ACPI objects", 2017-04-10), this patch enables
OvmfPkg/AcpiPlatformDxe to work entirely above the 4GB mark.

(An upcoming / planned aarch64 QEMU machine type will have no RAM under
4GB at all. Plus, moving the allocations higher is beneficial to the
current "virt" machine type as well; in Ard's words: "having all firmware
allocations inside the same 1 GB (or 512 MB for 64k pages) frame reduces
the TLB footprint".)

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Suggested-by: Igor Mammedov <imammedo@redhat.com>
Suggested-by: Gerd Hoffmann <kraxel@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>