- nr_ulsim supports multiple DMRS configurations

An avx2 instruction in idft4096 introduced segfault sometimes

In 3/4 sampling mode, the OFDM symbol size is _not_ a power of two (e.g. 1536 instead of 2048).
In this case it is _not_ OK to calculate the modulus using a binary AND, it _must_ use either the actul modulus operator (%) using an integer division,
or a _correct_ if statement or tertianary operator like this:

re_offset = (re_offset + 4 >= ue->frame_parms.ofdm_symbol_size) ? (re_offset + 4 - ue->frame_parms.ofdm_symbol_size) : (re_offset + 4);

But of course using the actual modulus operator is much more readable and surely not much slower:

re_offset = (re_offset + 4) % ue->frame_parms.ofdm_symbol_size;

Added the following folder:
- ../openair1/PHY/NR_ESTIMATION/

Added the following file to CMakelists.txt:
- ../openair1/PHY/NR_ESTIMATION/nr_ul_channel_estimation.c

Added the following functions:
- nr_pusch_dmrs_rx
- nr_gold_pusch
- nr_ulsch_channel_level
- nr_ulsch_channel_compensation
- nr_ulsch_scale_channel is commented out (I think only used for downlink)

Changes from Khalid Ahmed Mahmoud Mohamed:
- nr_pusch_channel_estimation is used
- nr_ulsch_scale_channel is used
- nr_ulsch_channel_level is used
- nr_ulsch_channel_compensation is used
- multiple logging options for channel and signal magnitude

Added the following folder:
- ../openair1/PHY/NR_ESTIMATION/

Added the following file to CMakelists.txt:
- ../openair1/PHY/NR_ESTIMATION/nr_ul_channel_estimation.c

Added the following functions:
- nr_pusch_dmrs_rx
- nr_gold_pusch
- nr_ulsch_channel_level
- nr_ulsch_channel_compensation
- nr_ulsch_scale_channel is commented out (I think only used for downlink)

Changes from Khalid Ahmed Mahmoud Mohamed:
- nr_pusch_channel_estimation is used
- nr_ulsch_scale_channel is used
- nr_ulsch_channel_level is used
- nr_ulsch_channel_compensation is used
- multiple logging options for channel and signal magnitude