ArmPlatformPkg/NorFlashDxe: accept both non-secure and secure varstore GUIDs

Now that the generic Variable Runtime DXE code no longer distinguishes
between gEfiVariableGuid and gEfiAuthenticatedVariableGuid in the varstore
FV header, we can relax the check in the NOR flash driver to accept either
GUID regardless of whether we are running a secure boot capable build or not.

This also means we can always use gEfiAuthenticatedVariableGuid when we
encounter an empty NOR flash that needs to be initialized before use. So
remove the mNorFlashVariableGuid global from the shared code and from both
versions of NorFlashDxe.inf. This essentially collapses the two drivers into
a single one, which means we can remove NorFlashAuthenticatedDxe entirely
in a subsequent patch.

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

ArmPlatformPkg/Drivers/NorFlashDxe/NorFlashDxe.h

@@ -152,8 +152,6 @@ struct _NOR_FLASH_INSTANCE {
   NOR_FLASH_DEVICE_PATH               DevicePath;
 };
 
-extern CONST EFI_GUID* CONST          mNorFlashVariableGuid;
-
 EFI_STATUS
 NorFlashReadCfiData (
   IN  UINTN                   DeviceBaseAddress,