ARM: zynq: DT: Add 'clock-latency' property

Specify the 'clock-latency' property to avoid certain cpufreq governors
from refusing to work with the following error:
  ondemand governor failed, too long transition latency of HW, fallback to performance governor

Reported-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Tested-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/boot/dts/zynq-7000.dtsi

@@ -24,6 +24,7 @@
 			device_type = "cpu";
 			reg = <0>;
 			clocks = <&clkc 3>;
+			clock-latency = <1000>;
 			operating-points = <
 				/* kHz    uV */
 				666667  1000000