Platform/ARM: drop per-bank NOR flash GUIDs

Remove the GUID definitions from the NOR flash bank structure: the
driver no longer uses them.

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