cpufreq: imx-cpufreq-dt: Add "cpu-supply" property check

The cpufreq-dt driver allows cpufreq driver enabled without valid
regulator assigned, however, all i.MX platforms using cpufreq-dt
driver now require valid regulator, add "cpu-supply" property check
to avoid i.MX platforms' cpufreq enabled without valid regulator
and lead to system unstable.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/cpufreq/imx-cpufreq-dt.c

@@ -31,6 +31,9 @@ static int imx_cpufreq_dt_probe(struct platform_device *pdev)
 	int speed_grade, mkt_segment;
 	int ret;
 
+	if (!of_find_property(cpu_dev->of_node, "cpu-supply", NULL))
+		return -ENODEV;
+
 	ret = nvmem_cell_read_u32(cpu_dev, "speed_grade", &cell_value);
 	if (ret)
 		return ret;