dts: mpc512x: add clock related device tree specs

this addresses the clock driver aka provider's side of clocks
- introduce a 'clocks' subtree with an 'osc' node for the crystal
or oscillator SoC input (fixed frequency)
- the 'clock@f00' clock-control-module node references the 'osc' for
its input, and is another provider for all the clocks which the
CCM component manages
- prepare for future references to clocks from peripheral nodes
by means of the <&clks ID> syntax and symbolic ID names which a
header file provides
- provide default values with 33MHz oscillator frequency in the
common include (the 66MHz IPS bus already was there), and add
override values for the ifm AC14xx board which deviates from
the reference design (25MHz xtal, 80MHz IPS bus)

Cc: Rob Herring <[e-mail]>
Cc: Pawel Moll <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Stephen Warren <[e-mail]>
Cc: Ian Campbell <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Reviewed-by: Mike Turquette <[e-mail]>
Signed-off-by: Gerhard Sittig <[e-mail]>
Signed-off-by: Anatolij Gustschin <[e-mail]>

arch/powerpc/boot/dts/ac14xx.dts

···
 		};
 	};
 
+	clocks {
+		osc {
+			clock-frequency = <25000000>;
+		};
+	};
+
 	soc@80000000 {
+		bus-frequency = <80000000>;	/* 80 MHz ips bus */
 
 		clock@f00 {
 			compatible = "fsl,mpc5121rev2-clock", "fsl,mpc5121-clock";

arch/powerpc/boot/dts/mpc5121.dtsi

···
  * option) any later version.
  */
 
+#include <dt-bindings/clock/mpc512x-clock.h>
+
 /dts-v1/;
 
 / {
···
 		ranges = <0x0 0x0 0xfc000000 0x04000000>;
 	};
 
+	clocks {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		osc: osc {
+			compatible = "fixed-clock";
+			#clock-cells = <0>;
+			clock-frequency = <33000000>;
+		};
+	};
+
 	soc@80000000 {
 		compatible = "fsl,mpc5121-immr";
 		#address-cells = <1>;
···
 		};
 
 		/* Clock control */
-		clock@f00 {
+		clks: clock@f00 {
 			compatible = "fsl,mpc5121-clock";
 			reg = <0xf00 0x100>;
+			#clock-cells = <1>;
+			clocks = <&osc>;
+			clock-names = "osc";
 		};
 
 		/* Power Management Controller */