ArmVirtPkg/XenRelocatablePlatformLib: rewrite DTB memory node retrieval in C

ArmVirtPkg/XenRelocatablePlatformLib: rewrite DTB memory node retrieval in C

Parsing the DTB early on using a handcoded assembly routine is a pointless
waste of brain cycles, since the UEFI firmware always executes from RAM
under Xen. So instead, set up a temporary stack in the memory region at the
beginning of the image, and use the libfdt C library.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19330 6f19259b-4bc3-4df7-8a09-765794883524