Add master clock nodes generated by crystal oscillators.
  PH1-sLD3, PH1-LD4: 24.576 MHz
  PH1-Pro4, ProXstream2: 25.000 MHz
  PH1-Pro5: 20.000 MHz
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
 /include/ "skeleton.dtsi"
 
 / {
+       clocks {
+               refclk: ref {
+                       #clock-cells = <0>;
+                       compatible = "fixed-clock";
+               };
+       };
+
        soc: soc {
                compatible = "simple-bus";
                #address-cells = <1>;
 
        };
 };
 
+&refclk {
+       clock-frequency = <24576000>;
+};
+
 &serial0 {
        clock-frequency = <36864000>;
 };
 
        };
 };
 
+&refclk {
+       clock-frequency = <25000000>;
+};
+
 &serial0 {
        clock-frequency = <73728000>;
 };
 
        };
 };
 
+&refclk {
+       clock-frequency = <20000000>;
+};
+
 &serial0 {
        clock-frequency = <73728000>;
 };
 
        };
 
        clocks {
+               refclk: ref {
+                       #clock-cells = <0>;
+                       compatible = "fixed-clock";
+                       clock-frequency = <24576000>;
+               };
+
                arm_timer_clk: arm_timer_clk {
                        #clock-cells = <0>;
                        compatible = "fixed-clock";
 
        };
 };
 
+&refclk {
+       clock-frequency = <25000000>;
+};
+
 &serial0 {
        clock-frequency = <80000000>;
 };
 
        };
 };
 
+&refclk {
+       clock-frequency = <25000000>;
+};
+
 &serial0 {
        clock-frequency = <88900000>;
 };