dt-bindings: cpufreq: remove stale arm_big_little_dt entry

Most of the ARM platforms used v2 OPP bindings to support big-little
configurations. This arm_big_little_dt binding is incomplete and was
never used.

Commit f174e49e (cpufreq: remove unused arm_big_little_dt driver)
removed the driver supporting this binding, but the binding was left
unnoticed, so let's get rid of it now.

Fixes: f174e49e (cpufreq: remove unused arm_big_little_dt driver)
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/devicetree/bindings/cpufreq/arm_big_little_dt.txt

-Generic ARM big LITTLE cpufreq driver's DT glue
------------------------------------------------
-
-This is DT specific glue layer for generic cpufreq driver for big LITTLE
-systems.
-
-Both required and optional properties listed below must be defined
-under node /cpus/cpu@x. Where x is the first cpu inside a cluster.
-
-FIXME: Cpus should boot in the order specified in DT and all cpus for a cluster
-must be present contiguously. Generic DT driver will check only node 'x' for
-cpu:x.
-
-Required properties:
-- operating-points: Refer to Documentation/devicetree/bindings/opp/opp.txt
-  for details
-
-Optional properties:
-- clock-latency: Specify the possible maximum transition latency for clock,
-  in unit of nanoseconds.
-
-Examples:
-
-cpus {
-	#address-cells = <1>;
-	#size-cells = <0>;
-
-	cpu@0 {
-		compatible = "arm,cortex-a15";
-		reg = <0>;
-		next-level-cache = <&L2>;
-		operating-points = <
-			/* kHz    uV */
-			792000  1100000
-			396000  950000
-			198000  850000
-		>;
-		clock-latency = <61036>; /* two CLK32 periods */
-	};
-
-	cpu@1 {
-		compatible = "arm,cortex-a15";
-		reg = <1>;
-		next-level-cache = <&L2>;
-	};
-
-	cpu@100 {
-		compatible = "arm,cortex-a7";
-		reg = <100>;
-		next-level-cache = <&L2>;
-		operating-points = <
-			/* kHz    uV */
-			792000  950000
-			396000  750000
-			198000  450000
-		>;
-		clock-latency = <61036>; /* two CLK32 periods */
-	};
-
-	cpu@101 {
-		compatible = "arm,cortex-a7";
-		reg = <101>;
-		next-level-cache = <&L2>;
-	};
-};