Platforms/AMD/Cello: reduce core count to 4
Platforms/AMD/Cello: reduce core count to 4

Update the NUM_CORES define to accurately reflect the core count
of the SoC part used on the CelloBoard.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <66d3c5fdaeea7ff1f996ad04f2c45e08ab38e2f5@linaro.org>
Reviewed-by: Leif Lindholm <a613079f0455438b29e28a9c5b9eb3779a81a33a@linaro.org>

jlinton/OpenPlatformPkg,jlinton/OpenPlatformPkg