ArmPlatformPkg: add support for FV embedded device tree blobs

ArmPlatformPkg: add support for FV embedded device tree blobs

This adds support to the ArmVExpressPkg platforms to load their
device tree binary from a Firmware Volume if one is found that
matches the current platform. If none is found, the existing
logic to find a FDT by name from a file system is retained as
a fallback.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17359 6f19259b-4bc3-4df7-8a09-765794883524