While Google created an API in Android Lollipop that exposes RAW images from the camera, Android leaves it up the each phone manufacturer as to whether they will make the camera RAW available to the user. Therefore, to gain access to RAW images, you need the phone manufacturer to enable it, and software to take advantage of it. And yes, it is possible for a phone manufacturer to enable this via a software update, since it is part of the Android Lollipop build.

For software, Camera FV-5, an Android Lollipop app, captures photos in Adobe RAW (DNG) format. This is taking advantage of the RAW support that is available in Android Lollipop.

AS mentioned, just having Lollipop and Camera FV-5 isn't enough either, your camera manufacturer must also make this API available as well. At the moment, only the Nexus 5 and Nexus 6 make the API available, as does the OnePlus One. More info You likely do not see Camera FV-5 in the Play store because it is not compatible with your phone model.

The OnePlus One, being an Android-based Cyanogen OS phone, does not require the Camera FV-5 app, as RAW is enabled out of the box.