ArmVirtPkg/ArmVirtQemu: switch secure boot build to NorFlashDxe

ArmVirtPkg/ArmVirtQemu: switch secure boot build to NorFlashDxe

There is no longer a reason to use a different implementation of
NorFlashDxe for secure boot builds now that the varstore FV header can
carry either gEfiVariableGuid or gEfiAuthenticatedVariableGuid, and the
dependent code has been updated to deal with that. So move the secure
boot capable builds to the common NorFlashDxe.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>