hps: use nextpnr router1 by default (not in parallel)
hps: use nextpnr router1 by default (not in parallel)

With the latest nextpnr improvements, router1 reliably produces good
results without needing to spawn a larger number of nextpnr processes.

Signed-off-by: Dan Callaghan <c6268a61d01f53ee8e097a439feb27b30b61efda@google.com>

google/CFU-Playground,google/CFU-Playground,google/CFU-Playground,google/CFU-Playground