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/ArmVirtQemu.dsc

@@ -34,6 +34,7 @@
   # -D FLAG=VALUE
   #
   DEFINE SECURE_BOOT_ENABLE      = FALSE
+  DEFINE PURE_ACPI_BOOT_ENABLE   = FALSE
 
 !include ArmVirtPkg/ArmVirt.dsc.inc
 
@@ -94,6 +95,10 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutGopSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutUgaSupport|FALSE
 
+!if $(PURE_ACPI_BOOT_ENABLE) == TRUE
+  gArmVirtTokenSpaceGuid.PcdPureAcpiBoot|TRUE
+!endif
+
 [PcdsFixedAtBuild.common]
   gArmPlatformTokenSpaceGuid.PcdCoreCount|1
 !if $(ARCH) == AARCH64