This is necessary in order to properly "emulate" the previous implementation
of the gc_sync_ffs module.

Furthermore, a "new" module has been introduced, the gc_edge_detect, which
combines positive and negative pulse edge detection. gc_negedge and gc_posedge
have been rewritten to use internally the new gc_edge_detect.
Signed-off-by: Dimitris Lampridis <dimitris.lampridis@cern.ch>