OvmfPkg: AcpiPlatformDxe: implement QEMU's full ACPI table loader interface

Recent changes in the QEMU ACPI table generator have shown that our
limited client for that interface is insufficient and/or brittle.

Implement the full interface utilizing OrderedCollectionLib for addressing
fw_cfg blobs by name.

In order to stay compatible with EFI_ACPI_TABLE_PROTOCOL, we don't try to
identify QEMU's RSD PTR and link it into the UEFI system configuration
table. Instead, once all linker/loader commands have been processed, we
process the AddPointer commands for a second time.

In the second pass, we look at the targets of these pointer commands. The
key idea (by Michael Tsirkin) is that any ACPI interpreter will only be
able to locate ACPI tables by following absolute pointers, hence QEMU's
set of AddPointer commands will cover all of the ACPI tables (and more,
see below).

Some of QEMU's AddPointer commands (ie. some fields in ACPI tables) may
point to areas in fw_cfg blobs that are not ACPI tables themselves.
Examples are the BGRT.ImageAddress field, and the TCPA.LASA field. We tell
these apart from ACPI tables by performing the following checks on pointer
target "candidates":
- length check against minimum ACPI table size, and remaining blob size
- checksum verification.

If a target area looks like an ACPI table, and is different from RSDT and
DSDT (which EFI_ACPI_TABLE_PROTOCOL handles internally), we install the
table (at which point EFI_ACPI_TABLE_PROTOCOL creates a deep copy of the
relevant segment of the pointed-to fw_cfg blob).

Simultaneously, we keep account if each fw_cfg blob has ever been
referenced as the target of an AddPointer command without that AddPointer
command actually identifying an ACPI table. In this case the containing
fw_cfg file (of AcpiNVS memory type) must remain around forever, because
we never install that area with EFI_ACPI_TABLE_PROTOCOL, but some field in
some ACPI table that we *do* install still references it, by the absolute
address that we've established during the first pass.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16158 6f19259b-4bc3-4df7-8a09-765794883524

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