kernel-module-cdce925: Move into kernel

The clock synth can be loaded early, so integrate it into the kernel.
fpga-image.inc: Use update-alternatives

Multiple FPGA bitstreams can be generated for a single machine. Separate
them using update-alternatives. This also allows to install multiple
bitstreams and "switch" between them.

Remove the bitstreams from the sysroot install, so they will not conflict
during build.