MIPS: mscc: add PCB120 to the ocelot fitImage

PCB120 and PCB123 are both development boards based on Microsemi Ocelot
so let's use the same fitImage for both.

Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20871/
Cc: ralf@linux-mips.org
Cc: jhogan@kernel.org
Cc: robh+dt@kernel.org
Cc: mark.rutland@arm.com
Cc: davem@davemloft.net
Cc: andrew@lunn.ch
Cc: f.fainelli@gmail.com
Cc: allan.nielsen@microchip.com
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: thomas.petazzoni@bootlin.com
Cc: antoine.tenart@bootlin.com