EmbeddedPkg: add DtPlatformDtbLoaderLib library class

To abstract the way a platform reasons about which DTB is appropriate,
and the way it ultimately supplies the DTB image, introduce a new library
class to encapsulate this functionality.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

EmbeddedPkg/EmbeddedPkg.dec

@@ -45,6 +45,7 @@
   GdbSerialLib|Include/Library/GdbSerialLib.h
   DebugAgentTimerLib|Include/Library/DebugAgentTimerLib.h
 
+  DtPlatformDtbLoaderLib|Include/Library/DtPlatformDtbLoaderLib.h
 
 [Guids.common]
   gEmbeddedTokenSpaceGuid       = { 0xe0d8ca17, 0x4276, 0x4386, { 0xbb, 0x79, 0x48, 0xcb, 0x81, 0x3d, 0x3c, 0x4f }}

EmbeddedPkg/Include/Library/DtPlatformDtbLoaderLib.h

@@ -0,0 +1,39 @@
+/** @file
+*
+*  Copyright (c) 2017, Linaro, Ltd. All rights reserved.
+*
+*  This program and the accompanying materials
+*  are licensed and made available under the terms and conditions of the BSD License
+*  which accompanies this distribution.  The full text of the license may be found at
+*  http://opensource.org/licenses/bsd-license.php
+*
+*  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+*  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+*
+**/
+
+#ifndef __DT_PLATFORM_DTB_LOADER_LIB_H__
+#define __DT_PLATFORM_DTB_LOADER_LIB_H__
+
+#include <Uefi/UefiBaseType.h>
+
+/**
+  Return a pool allocated copy of the DTB image that is appropriate for
+  booting the current platform via DT.
+
+  @param[out]   Dtb                   Pointer to the DTB copy
+  @param[out]   DtbSize               Size of the DTB copy
+
+  @retval       EFI_SUCCESS           Operation completed successfully
+  @retval       EFI_NOT_FOUND         No suitable DTB image could be located
+  @retval       EFI_OUT_OF_RESOURCES  No pool memory available
+
+**/
+EFI_STATUS
+EFIAPI
+DtPlatformLoadDtb (
+  OUT   VOID        **Dtb,
+  OUT   UINTN       *DtbSize
+  );
+
+#endif