Add PLATFORM_HAS_RADIO in Sky Platform

In order to use the er-server-example Radio resource it is required that the platform defines that it has a radio. This line might be required in other platforms.
Merge pull request #745 from PaulCorbalan/patch-1

Add PLATFORM_HAS_RADIO in Sky Platform
Merge commit '35b6032c645cd636f7fb0d5e93a45e1952128eb0' into HEAD