ArmPlatformPkg/NorFlashDxe: prepare for devicepath format change

A subsequent patch will change the layout of devicepath nodes
produced by this driver. In preparation, make some tweaks to
the code to use a packed struct for the devicepath and to pass
the device index to NorFlashCreateInstance(). These are cosmetic
changes only, the resulting binaries should be identical.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Thomas Abraham <thomas.abraham@arm.com>

ArmPlatformPkg/Drivers/NorFlashDxe/NorFlashDxe.h

@@ -122,10 +122,12 @@
 
 typedef struct _NOR_FLASH_INSTANCE                NOR_FLASH_INSTANCE;
 
+#pragma pack (1)
 typedef struct {
   VENDOR_DEVICE_PATH                  Vendor;
   EFI_DEVICE_PATH_PROTOCOL            End;
 } NOR_FLASH_DEVICE_PATH;
+#pragma pack ()
 
 struct _NOR_FLASH_INSTANCE {
   UINT32                              Signature;