spi: rockchip: add description for px30

Add "rockchip,px30-spi", "rockchip,rk3066-spi" for spi on px30 platform.

Signed-off-by: Liang Chen <cl@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-rockchip.txt

@@ -7,6 +7,7 @@ Required Properties:
 
 - compatible: should be one of the following.
     "rockchip,rv1108-spi" for rv1108 SoCs.
+    "rockchip,px30-spi", "rockchip,rk3066-spi" for px30 SoCs.
     "rockchip,rk3036-spi" for rk3036 SoCS.
     "rockchip,rk3066-spi" for rk3066 SoCs.
     "rockchip,rk3188-spi" for rk3188 SoCs.