Create binary voice string archive on target.

Create binary voice string archive on target.

Extend genlang to create files holding the voice strings in a binary format
similar to lng. Create such files for all languages during a normal build, put
them in a zip file and add them to rockbox.zip so they are installed with a
main build.

Creating a voice file requires access to the voice strings, which are currently
not distributed with Rockbox. Therefore it is necessary to either have access
to the source code of the installed build or to use a build the genlang service
on rockbox.org can retrieve the strings for, making it impossible for normal
users to generate a voice file for custom builds, test builds and older builds
that aren't supported by the rockbox.org script. It also requires a network
connection when creating voice files with Rockbox Utility even if creating a
voice file by itself isn't network related.

Furthermore, putting the voice strings on the target is also a prerequisite for
eventually supporting a TTS on the player.

Strip voice strings path.

Change-Id: Ic2f86130909b3b257986a348e5cfcf618c4500c3