samples/drivers/adc: Few fixes for use with twister

Add some changes to adc sample to enable valid verdict generation
using twister:
-Replace 'single_line' keyword with correct 'one_line'
-Remove parenthesis from the sample output to enable regex verdict
-Add timeout to save time in execution

Additionally, add support for disco_l475_iot1.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>

samples/drivers/adc/boards/disco_l475_iot1.overlay

@@ -0,0 +1,12 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Copyright (c) 2020 Linaro Limited
+ */
+
+/ {
+	zephyr,user {
+		/* adjust channel number according to pinmux in board.dts */
+		io-channels = <&adc1 5>;
+	};
+};

samples/drivers/adc/sample.yaml

@@ -4,9 +4,10 @@ tests:
   sample.drivers.adc:
     tags: ADC
     depends_on: adc
-    platform_allow: nucleo_l073rz
+    platform_allow: nucleo_l073rz disco_l475_iot1
     harness: console
+    timeout: 10
     harness_config:
-      type: single_line
+      type: one_line
       regex:
-        - "ADC reading(s): (.*)"
+        - "ADC reading: (.*)"

samples/drivers/adc/src/main.c

@@ -98,7 +98,7 @@ void main(void)
 			return;
 		}
 
-		printk("ADC reading(s):");
+		printk("ADC reading:");
 		for (uint8_t i = 0; i < ADC_NUM_CHANNELS; i++) {
 			int32_t raw_value = sample_buffer[i];