Extend device with sleep functionality

This changeset adds the ability to sleep on the device via a
device.sleep() method. This invokes sleep on the target device. This
is useful for situations where the passage of time on the target
device does not match that of the host, e.g., gem5.

This changeset also updates a number of workloads to use this new
sleep method.

wlauto/workloads/thechase/__init__.py

@@ -14,8 +14,6 @@
 #
 
 # pylint: disable=E1101
-import time
-
 from wlauto import ApkWorkload, Parameter
 
 
@@ -42,4 +40,4 @@ class TheChase(ApkWorkload):
     ]
 
     def run(self, context):
-        time.sleep(self.duration)
+        self.device.sleep(self.duration)