adding missing supported_platforms attributes.

Bbench only works on Android. It should advertise that fact by setting
supported_platforms to ['android'].
Telemetry is a Chrome browser workload that is only supported on
ChromeOS and Android.

wlauto/workloads/bbench/__init__.py

@@ -74,6 +74,8 @@ class BBench(Workload):
         Alias('bbench_with_audio', with_audio=True),
     ]
 
+    supported_platforms = ['android']
+
     def setup(self, context):  # NOQA
         self.bbench_on_device = '/'.join([self.device.working_directory, 'bbench'])
         self.bbench_server_on_device = os.path.join(self.device.working_directory, BBENCH_SERVER_NAME)

wlauto/workloads/telemetry/__init__.py

@@ -88,6 +88,8 @@ class Telemetry(Workload):
 
     """
 
+    supported_platforms = ['android', 'chromeos']
+
     parameters = [
         Parameter('run_benchmark_path', default=None,
                   description="""