Silicon/SynQuacer: drop per-bank NOR flash GUIDs

Give the SynQuacer NOR flash driver the same treatment as we gave the
one in ArmPlatformPkg: identify NOR flash banks by a single GUID
identifying the driver, and use indexes to identify each device instance
owned by the driver.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>