doc: Initial GP_DCMPREF/GP_DCMPMUX docs
doc: Initial GP_DCMPREF/GP_DCMPMUX docs

azonenberg/openfpga,rqou/openfpga,azonenberg/openfpga,rqou/openfpga,rqou/openfpga,rqou/openfpga,azonenberg/openfpga,azonenberg/openfpga,rqou/openfpga,azonenberg/openfpga