OvmfPkg/Xen: export search of RSDP into a library function

Xen and bhyve are placing ACPI tables into system memory. So, they can
share the same code. Therefore, create a new library which searches and
installs ACPI tables from system memory.

Signed-off-by: Corvin Köhne <corvink@FreeBSD.org>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>

OvmfPkg/Include/Library/AcpiPlatformLib.h

@@ -0,0 +1,24 @@
+/** @file
+  Copyright (c) 2023, Corvin Köhne <corvink@FreeBSD.org>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+/**
+  Searches and returns the address of the ACPI Root System Description Pointer (RSDP) in system memory.
+
+  @param  StartAddress        Start address of search range.
+  @param  EndAddress          End address of search range.
+  @param  RsdpPtr             Return pointer to RSDP.
+
+  @retval EFI_SUCCESS         RSDP successfully found.
+  @retval EFI_NOT_FOUND       Couldn't find RSDP.
+  @retval EFI_ABORTED         Invalid RSDP found.
+**/
+EFI_STATUS
+EFIAPI
+GetAcpiRsdpFromMemory (
+  IN UINT64                                         StartAddress,
+  IN UINT64                                         EndAddress,
+  OUT EFI_ACPI_2_0_ROOT_SYSTEM_DESCRIPTION_POINTER  **RsdpPtr
+  );