added mem mux for beamlet index in VHDL

...2_unb2b_sdp_station/src/vhdl/lofar2_unb2b_sdp_station.vhd

...b2b_sdp_station/src/vhdl/mmm_lofar2_unb2b_sdp_station.vhd

...dp_station/src/vhdl/qsys_lofar2_unb2b_sdp_station_pkg.vhd

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