Optimize LTE TM2 modulation
This adds optimizations for TM2 modulation (QPSK/16QAM/64QAM) in dlsch_modulation.c. Improves by around a factor of 4 from old code. Brings 20 MHz 2x2 TX times down to less than 500us for mcs28 100 PRBs.
Edited by Robert Schmidt