Remove the option to use the 200MHz PCI clock for the complete DMA engine to avoid compicating the design
and introducing too many alternatives that will need to be tested, now and in the future.

On the SPEC, it has been shown that with the latest modifications it is trivial to meet timing when using
a 125MHz (asynchronous to the PCI) clock for DMA.

Signed-off-by: Dimitris Lampridis <dimitris.lampridis@cern.ch>