tests/drivers/rtc: Add unit tests for RTC devices

This test suite adds tests for the following:

- Setting and getting time
- Validating time is incrementing correctly
- Validating behavior of alarms with callback disabled
- Validating behavior of alarms with callback enabled
- Validating update callback

The test suite uses the devicetree  alias rtc to find
the device to test.

Signed-off-by: Bjarki Arge Andreasen <baa@trackunit.com>

dts/bindings/rtc/rtc-device.yaml

@@ -0,0 +1,13 @@
+# Copyright (c) 2022 Bjarki Arge Andreasen
+# SPDX-License-Identifier: Apache-2.0
+
+include: base.yaml
+
+description: RTC device common bindings
+
+properties:
+  alarms-count:
+    type: int
+    required: true
+    description: |
+      Number of alarms supported by RTC device