Add REG_SDP_TBUF in vhdl and in yaml.

...far2_unb2c_sdp_station/lofar2_unb2c_sdp_station.fpga.yaml

applications/lofar2/libraries/sdp/hdllib.cfg

applications/lofar2/libraries/sdp/sdp.peripheral.yaml

applications/lofar2/libraries/sdp/src/vhdl/sdp_tbuf_pkg.vhd

...ions/lofar2/libraries/sdp/src/vhdl/sdp_tbuf_registers.vhd