EmbeddedPkg/FdtPlatformDxe: Add 'setfdt' EFI Shell command

EmbeddedPkg/FdtPlatformDxe: Add 'setfdt' EFI Shell command

The 'setfdt' EFI Shell command allows to define a new FDT
as the prefered one for development purposes. It allows to
trigger the run of the FDT installation process as well.

Please refer to the README.txt file for more comprehensive
description.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ronald Cron <Ronald.Cron@arm.com>
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16934 6f19259b-4bc3-4df7-8a09-765794883524