introduce UEFI specific counterpart to acpi_find_rsdp_address()
that will help to find RSDP address when [OA]VMF is used as
firmware. It requires guest firmware or other guest app to place
1Mb aligned UefiTestSupport structure (defined in this patch)
in RAM with UefiTestSupport::signature_guid set to
AB87A6B1-2034-BDA0-71BD-375007757785
For test app details see commit
  (09a274d8 tests: introduce "uefi-test-tools" with the BiosTablesTest UEFI app)

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Wei Yang <richardw.yang@linux.intel.com>
Message-Id: <1556808723-226478-9-git-send-email-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>