nexus: Bel search function for DCC placement
nexus: Bel search function for DCC placement

Signed-off-by: David Shah <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@ds0.me>

SymbiFlow/nextpnr,YosysHQ/nextpnr,YosysHQ/nextpnr,SymbiFlow/nextpnr,YosysHQ/nextpnr,SymbiFlow/nextpnr,YosysHQ/nextpnr,SymbiFlow/nextpnr