Add ram_equalizer_gains_cross register to QSYS.

...sys_lofar2_unb2c_sdp_station_ram_equalizer_gains_cross.ip

...2c_sdp_station/quartus/qsys_lofar2_unb2c_sdp_station.qsys

...dp_station/src/vhdl/qsys_lofar2_unb2c_sdp_station_pkg.vhd