samples: drivers: adc: add ADC example

This sample shows how to use the ADC API. Depending on the support of
sequential reads in the driver, 1 or 2 channels are read and printed.

A devicetree overlay is necessary to specify the used ADC channel(s).

Signed-off-by: Martin Jäger <martin@libre.solar>

samples/drivers/adc/sample.yaml

@@ -0,0 +1,12 @@
+sample:
+  name: ADC driver sample
+tests:
+  sample.drivers.adc:
+    tags: ADC
+    depends_on: adc
+    platform_allow: nucleo_l073rz
+    harness: console
+    harness_config:
+      type: single_line
+      regex:
+        - "ADC reading(s): (.*)"