dt-bindings: dma-engine: sifive,fu540: Add dma-channels property and modify compatible

Add dma-channels property, then we can determine how many channels there
by device tree, rather than statically defining it in PDMA driver.
In addition, we also modify the compatible for PDMA versioning scheme.
Signed-off-by: Zong Li <zong.li@sifive.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Suggested-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Link: https://lore.kernel.org/r/7cc9a7b5f7e6c28fc9eb172c441b5aed2159b8a0.1648461096.git.zong.li@sifive.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/dma/sifive,fu540-c000-pdma.yaml

@@ -28,7 +28,15 @@ allOf:
 properties:
   compatible:
     items:
-      - const: sifive,fu540-c000-pdma
+      - enum:
+          - sifive,fu540-c000-pdma
+      - const: sifive,pdma0
+    description:
+      Should be "sifive,<chip>-pdma" and "sifive,pdma<version>".
+      Supported compatible strings are -
+      "sifive,fu540-c000-pdma" for the SiFive PDMA v0 as integrated onto the
+      SiFive FU540 chip resp and "sifive,pdma0" for the SiFive PDMA v0 IP block
+      with no chip integration tweaks.
 
   reg:
     maxItems: 1
@@ -37,6 +45,12 @@ properties:
     minItems: 1
     maxItems: 8
 
+  dma-channels:
+    description: For backwards-compatibility, the default value is 4
+    minimum: 1
+    maximum: 4
+    default: 4
+
   '#dma-cells':
     const: 1
 
@@ -50,8 +64,9 @@ unevaluatedProperties: false
 examples:
   - |
     dma-controller@3000000 {
-      compatible = "sifive,fu540-c000-pdma";
+      compatible = "sifive,fu540-c000-pdma", "sifive,pdma0";
       reg = <0x3000000 0x8000>;
+      dma-channels = <4>;
       interrupts = <23>, <24>, <25>, <26>, <27>, <28>, <29>, <30>;
       #dma-cells = <1>;
     };