ArmPlatformPkg: Retire NorFlashDxe driver

The NorFlashDxe driver in ArmPlatformPkg was shared between development
platforms built by ARM Ltd, and virtual platforms that were once modeled
after Versatile Express, but have very little in common with actual bare
metal implementations.

Both sides have migrated to a domain specific version of the driver, so
we can retire the old one.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>