pytests: Add helpers to skip tests on the devkit and phone

pytests/boardtype.py

+# Board type related helpers
+
+
+def _get_board_type():
+    with open('/proc/device-tree/model') as f:
+        # model ends with a null byte
+        return f.readline().strip().strip('\00')
+
+
+def is_librem5():
+    return _get_board_type() == r'Purism Librem 5'
+
+
+def is_devkit():
+    return _get_board_type() == 'Purism Librem 5 devkit'
+
+
+if __name__ == '__main__':
+    print("Board: '{}'".format(_get_board_type()))
+    print('devkit: {}'.format(is_devkit()))
+    print('librem5: {}'.format(is_librem5()))