drivers: imx_tmu: Select polling-rate from cpu-thermal devicetree node

The polling rate is already specified in some devicetrees, like
imx8mp.dtsi for example, but was not selected so far. For the
trippoints, the cpu-thermal node is used. Also get the polling rate from
this node. Use the default of 5000ms if the polling rate should not be
specified in the devicetree.

NOTE: The polling rate from the devicetree will be used after this
patch. In imx8*.dtsi devicetrees the polling delay is set to 2000ms for
example.

Signed-off-by: Benjamin Hahn <B.Hahn@phytec.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/drivers/thermal/imx_tmu.c b/drivers/thermal/imx_tmu.c
index 4721cfb..c7fe0f0 100644
--- a/drivers/thermal/imx_tmu.c
+++ b/drivers/thermal/imx_tmu.c
@@ -570,12 +570,14 @@
 {
 	struct imx_tmu_plat *pdata = dev_get_plat(dev), *p_parent_data;
 	struct ofnode_phandle_args args;
-	ofnode trips_np;
+	ofnode trips_np, cpu_thermal_np;
 	int ret;
 
 	dev_dbg(dev, "%s\n", __func__);
 
-	pdata->polling_delay = IMX_TMU_POLLING_DELAY_MS;
+	cpu_thermal_np = ofnode_path("/thermal-zones/cpu-thermal");
+	pdata->polling_delay = ofnode_read_u32_default(cpu_thermal_np, "polling-delay",
+						       IMX_TMU_POLLING_DELAY_MS);
 
 	if (pdata->zone_node) {
 		pdata->regs = (union tmu_regs *)dev_read_addr_ptr(dev);