targets/r600/omx: convert to static/shared pipe-drivers

targets/r600/omx: convert to static/shared pipe-drivers

The r600 counterpart of previous commit - now the libomx-r600 is
built into the libomx-mesa library. Providing a single library per API.

v2: Include the radeon winsys only when there is a user for it.
v3: Correcly include the winsys. Now with extra brown bag :\

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.

Cc: Leo Liu <leo.liu@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>