EmbeddedPkg: introduce PlatformHasAcpiLib

Add the shorter-term library instance outlined in the previous patch to
EmbeddedPkg, so that we can imbue AcpiTableDxe with a protocol dependency
on EDKII_PLATFORM_HAS_ACPI_GUID.

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

EmbeddedPkg/Library/PlatformHasAcpiLib/PlatformHasAcpiLib.inf

@@ -0,0 +1,40 @@
+## @file
+# A hook-in library for MdeModulePkg/Universal/Acpi/AcpiTableDxe.
+#
+# Plugging this library instance into AcpiTableDxe makes
+# EFI_ACPI_TABLE_PROTOCOL and (if enabled) EFI_ACPI_SDT_PROTOCOL depend on the
+# platform's dynamic decision whether to expose an ACPI-based hardware
+# description to the operating system.
+#
+# Universal and platform specific DXE drivers that produce ACPI tables depend
+# on EFI_ACPI_TABLE_PROTOCOL / EFI_ACPI_SDT_PROTOCOL in turn.
+#
+# Copyright (C) 2017, Red Hat, Inc.
+#
+# 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.
+##
+
+[Defines]
+  INF_VERSION                    = 1.25
+  BASE_NAME                      = PlatformHasAcpiLib
+  FILE_GUID                      = 29beb028-0958-447b-be0a-12229235d77d
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = PlatformHasAcpiLib|DXE_DRIVER
+  CONSTRUCTOR                    = PlatformHasAcpiInitialize
+
+[Sources]
+  PlatformHasAcpiLib.c
+
+[Packages]
+  EmbeddedPkg/EmbeddedPkg.dec
+  MdePkg/MdePkg.dec
+
+[Depex]
+  gEdkiiPlatformHasAcpiGuid