MdePkg: Support FDT library.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4392
Add FDT support in EDK2 by submodule 3rd party libfdt
(https://github.com/devicetree-org/pylibfdt/tree/main/libfdt)
and refer to LibcLib implementation by Pedro.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Signed-off-by: Benny Lin <benny.lin@intel.com>
Acked-by: Pedro Falcato <pedro.falcato@gmail.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>

MdePkg/MdePkg.dec

@@ -289,6 +289,10 @@
   #
   ArmTrngLib|Include/Library/ArmTrngLib.h
 
+  ##  @libraryclass  Provides APIs for third-party library libfdt.
+  #
+  FdtLib|Include/Library/FdtLib.h
+
 [LibraryClasses.IA32, LibraryClasses.X64, LibraryClasses.AARCH64]
   ##  @libraryclass  Provides services to generate random number.
   #