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.
Added -p option to the list command. This alows filtering results by
supported platforms, e.g.
wa list workloads -p linux
Also adding missing supported_platforms attribute to various extensions.
If an extension does not have this attribute, the assumption is that it
is supported by all available platforms.
