vlc-ubuntu-raspberry: add an Ubuntu target to build for raspberry

This image contains headers to support MMAL and other hardware specific features.

No need to add Raspbian packages mixed with Debian native packages.

No need to install contrib packages. They can be built once with the proper version from contribs and used as prebuilt contribs later. Thus the image is smaller.

We do keep the Qt5 prebuilt as building from contribs on Linux has good chances of not working.

Also prebuild cmake and protobuf so they are not rebuilt each time.