BaseTools/Gcc ARM AARCH64: add support for building device tree binaries

BaseTools/Gcc ARM AARCH64: add support for building device tree binaries

While modern AARCH64 server systems use ACPI for describing the platform
topology to the OS, ARM systems and AARCH64 outside of the server space
mostly use device tree binaries, which are compiled from device tree
source files using the device tree compiler.

Currently, such source files and binaries may be kept in the EDK2 platform
trees, but are not integrated with the build, which means they need to be
kept in sync and recompiled manually, which is cumbersome.

So let's wire up BaseTools support for them: add tool definitions for the
DTC compiler and preprocessor flags that allow these source files to use
FixedPcd expressions and other macros defined by AutoGen.h

This way, a device tree binary can be built from source and emitted into
a FFS file automatically using something like:

  DeviceTree.inf:
    [Defines]
      INF_VERSION    = 0x00010019
      BASE_NAME      = SomePlatformDeviceTree
      FILE_GUID      = 25462CDA-221F-47DF-AC1D-259CFAA4E326 # gDtPlatformDefaultDtbFileGuid
      MODULE_TYPE    = USER_DEFINED
      VERSION_STRING = 1.0

    [Sources]
      SomePlatform.dts

    [Packages]
      MdePkg/MdePkg.dec

  SomePlatform.fdf:
    INF RuleOverride = DTB xxx/yyy/DeviceTree.inf

    [Rule.Common.USER_DEFINED.DTB]
      FILE FREEFORM = $(NAMED_GUID) {
        RAW BIN                |.dtb
      }

where it can be picked at runtime by the DTB loader that may refer to it
using gDtPlatformDefaultDtbFileGuid.

Note that this is very similar to how ACPI tables may be emitted into a
FFS file with a known GUID and picked up by AcpiTableDxe at runtime.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>