targets/omx-nouveau: convert to static/shared pipe-drivers

targets/omx-nouveau: convert to static/shared pipe-drivers

Similar to the vdpau/xvmc targets, we're going to convert the
multiple target libraries into a single one.

The library can be built with the relevant pipe-drivers
statically linked in, or loaded as shared modules.
Currently we default to static.

Note: Make sure to rebuild the .omxregister file, by executing
   $ omxregister-bellagio

If you have more than one omx library (libomx-radeonsi, libomx-r600),
make sure to temporary move the unused one. By the end of the series
there will be only one library that will be used for all hardware -
r600, radeonsi and nouveau.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>