OvmfPkg: Update AcpiPlatformDxe to alter MADT table

OvmfPkg: Update AcpiPlatformDxe to alter MADT table

RFC: https://bugzilla.tianocore.org/show_bug.cgi?id=3429

In TDX the guest firmware is designed to publish a multiprocessor-wakeup
structure to let the guest-bootstrap processor wake up guest-application
processors with a mailbox. The mailbox is memory that the guest firmware
can reserve so each guest virtual processor can have the guest OS send
a message to them. The address of the mailbox is recorded in the MADT
table. See [ACPI].

To maintain the simplicity of the AcpiPlatformDxe, the MADT ACPI table
will be altered in another driver (TdxDxe) by installing a protocol
to notify that the ACPI table provided by Qemu is ready. Then in TdxDxe
a notification functioin will be called to alter the MADT table to recorded
the mailbox address.

The protocol is gQemuAcpiTableNotifyProtocolGuid.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>