Revert "ArmVirtPkg/FdtClientDxe: make DT table installation !ACPI dependent"

This reverts commit 78c41ff519.

We realized that DXE drivers that are independent of AcpiPlatformDxe (that
is, independent of QEMU's ACPI generation), such as RamDiskDxe and
BootGraphicsResourceTableDxe, may produce and/or manipulate ACPI tables,
at driver dispatch or even at Ready To Boot.

This makes it unsafe for us to check for ACPI presence in the UEFI system
config table in a Ready To Boot callback, in order to decide about
exposing the DT.

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>

ArmVirtPkg/FdtClientDxe/FdtClientDxe.c

@@ -17,11 +17,9 @@
 #include <Library/DebugLib.h>
 #include <Library/UefiDriverEntryPoint.h>
 #include <Library/UefiBootServicesTableLib.h>
-#include <Library/UefiLib.h>
 #include <Library/HobLib.h>
 #include <libfdt.h>
 
-#include <Guid/Acpi.h>
 #include <Guid/EventGroup.h>
 #include <Guid/Fdt.h>
 #include <Guid/FdtHob.h>
@@ -318,16 +316,12 @@ OnReadyToBoot (
   )
 {
   EFI_STATUS      Status;
-  VOID            *Table;
 
-  //
-  // Only install the FDT as a configuration table if we are not exposing
-  // ACPI 2.0 (or later) tables. Note that the legacy ACPI table GUID has
-  // no meaning on ARM since we need at least ACPI 5.0 support, and the
-  // 64-bit ACPI 2.0 table GUID is mandatory in that case.
-  //
-  Status = EfiGetSystemConfigurationTable (&gEfiAcpi20TableGuid, &Table);
-  if (EFI_ERROR (Status) || Table == NULL) {
+  if (!FeaturePcdGet (PcdPureAcpiBoot)) {
+    //
+    // Only install the FDT as a configuration table if we want to leave it up
+    // to the OS to decide whether it prefers ACPI over DT.
+    //
     Status = gBS->InstallConfigurationTable (&gFdtTableGuid, mDeviceTreeBase);
     ASSERT_EFI_ERROR (Status);
   }