dt-bindings: clk: mpfs document msspll dri registers

As there are two sections of registers that are responsible for clock
configuration on the PolarFire SoC: add the dynamic reconfiguration
interface section to the binding & describe what each of the sections
are used for.

Fixes: 2145bb687e3f ("dt-bindings: clk: microchip: Add Microchip PolarFire host binding")
Reviewed-by: Daire McNamara <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Conor Dooley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Acked-by: Palmer Dabbelt <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>

Documentation/devicetree/bindings/clock/microchip,mpfs.yaml

···
     const: microchip,mpfs-clkcfg
 
   reg:
-    maxItems: 1
+    items:
+      - description: |
+          clock config registers:
+          These registers contain enable, reset & divider tables for the, cpu,
+          axi, ahb and rtc/mtimer reference clocks as well as enable and reset
+          for the peripheral clocks.
+      - description: |
+          mss pll dri registers:
+          Block of registers responsible for dynamic reconfiguration of the mss
+          pll
 
   clocks:
     maxItems: 1
···
             #size-cells = <2>;
             clkcfg: clock-controller@20002000 {
                 compatible = "microchip,mpfs-clkcfg";
-                reg = <0x0 0x20002000 0x0 0x1000>;
+                reg = <0x0 0x20002000 0x0 0x1000>, <0x0 0x3E001000 0x0 0x1000>;
                 clocks = <&ref>;
                 #clock-cells = <1>;
         };