arm64: dts: sprd: use new 'dma-channels' property

The '#dma-channels' property was deprecated in favor of one defined by
generic dma-common DT bindings.  Add new property while keeping old one
for backwards compatibility.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Baolin Wang <baolin.wang7@gmail.com>
Link: https://lore.kernel.org/r/20220516142857.6419-4-krzysztof.kozlowski@linaro.org'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm64/boot/dts/sprd/whale2.dtsi

@@ -126,7 +126,9 @@ ap_dma: dma-controller@20100000 {
 				reg = <0 0x20100000 0 0x4000>;
 				interrupts = <GIC_SPI 42 IRQ_TYPE_LEVEL_HIGH>;
 				#dma-cells = <1>;
+				/* For backwards compatibility: */
 				#dma-channels = <32>;
+				dma-channels = <32>;
 				clock-names = "enable";
 				clocks = <&apahb_gate CLK_DMA_EB>;
 			};
@@ -272,7 +274,9 @@ agcp_dma: dma-controller@41580000 {
 				compatible = "sprd,sc9860-dma";
 				reg = <0 0x41580000 0 0x4000>;
 				#dma-cells = <1>;
+				/* For backwards compatibility: */
 				#dma-channels = <32>;
+				dma-channels = <32>;
 				clock-names = "enable", "ashb_eb";
 				clocks = <&agcp_gate CLK_AGCP_DMAAP_EB>,
 				       <&agcp_gate CLK_AGCP_AP_ASHB_EB>;