riscv: dts: Add dma-channels property and modify compatible

Add dma-channels property, then we can determine how many channels there
by device tree, in addition, we add the pdma versioning scheme for
compatible.
Signed-off-by: NZong Li <zong.li@sifive.com>
Reviewed-by: NPalmer Dabbelt <palmer@rivosinc.com>
Acked-by: NPalmer Dabbelt <palmer@rivosinc.com>
Acked-by: NConor Dooley <conor.dooley@microchip.com>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>
Signed-off-by: NPalmer Dabbelt <palmer@rivosinc.com>

arch/riscv/boot/dts/sifive/fu540-c000.dtsi

@@ -168,11 +168,12 @@
 			status = "disabled";
 		};
 		dma: dma@3000000 {
-			compatible = "sifive,fu540-c000-pdma";
+			compatible = "sifive,fu540-c000-pdma", "sifive,pdma0";
 			reg = <0x0 0x3000000 0x0 0x8000>;
 			interrupt-parent = <&plic0>;
 			interrupts = <23>, <24>, <25>, <26>, <27>, <28>, <29>,
 				     <30>;
+			dma-channels = <4>;
 			#dma-cells = <1>;
 		};
 		uart1: serial@10011000 {