ArmPlatformPkg/Bds: Remove any use of the "Fdt" UEFI variable

ArmPlatformPkg/Bds: Remove any use of the "Fdt" UEFI variable

Remove the option to update the "Fdt" UEFI variable in the ARM BDS as
the "setfdt" EFI Shell command provides this service from now.

Remove the use of this variable in the legacy kernel boot loader and
use the FDT installed in the configuration table instead.

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@16940 6f19259b-4bc3-4df7-8a09-765794883524