added no_DTX function to eNB. This fills the TX subframes which have no PDSCH with a fake pdsch. It avoids switching between TX/RX in TDD systems during the DL periods.

MR945 : nr prach fr2
- Introduction of the PRACH frontend for FR2 (120kHz SCS, 32 and 66 PRB). 
- Tested with nr_prachsim and testcases added to test_case_list.xml also included some fixes for FR1, 
when prach occasion > 0 (small difference in Ncp)

MR950 : DL and UL PTRS for 5G NR

MR971 : Correct NDI + Minor MAC subPDU handling improvements
Fixes the issue : Ping in develop was unusually high (70+ms). The issue was that TA was scheduled in the second slot (of the two we currently schedule), but NDI was toggled for the first one. 
Other improvements:
- Correctly put padding MAC subPDU
- Only use subPDU DLSCH long header if length >= 256B
- Calculate TBS in DL pre-processor considering header and TA CE overhead.
- Improve some of the logging (LOG_D)
- re-enable TA

MR970 : uci gnb mac functions file
- Moved gNB MAC UCI related functions in a new file

MR972 : Bugfix nr rate matching assertion
- Fixes the assertion happening in rate matching of pdsch during iperf test.

MR975 : File openning in rrc_gNB_internal
- Only allow file opening in rrc_gNB-internal.c in phytest mode

MR977 : NR UE DCI sanity checks and fixes
These changes resolve a few stability issues and errors in NR UE
- Added sanity check for pucch_resource_indicator received in DL DCI, which resolves SEGV in select_pucch_resource() and check_pucch_format()
- Additional sanity checks included to catch false or erroneous DCI received
- Wrong MCS table calculation and error in accessing ul_config_request at UE resolved

Conflicts:
	openair1/PHY/NR_TRANSPORT/nr_dlsch.c
	openair1/PHY/NR_UE_ESTIMATION/nr_dl_channel_estimation.c
	openair1/PHY/NR_UE_TRANSPORT/nr_dlsch_demodulation.c
	openair1/SCHED_NR_UE/phy_procedures_nr_ue.c
	openair2/RRC/NR/nr_rrc_proto.h

Merge remote-tracking branch 'origin/bugfix-nr-rate-matching-assertion' into integration_2020_wk48_2

MR932 : Nr sa ngap rrc wk42 
- Initial implementation of NGAP and RRC extensions for SA
 
MR956 : Correct use of ssb_position bitmaps  

MR958 : 5G NR Downlink DMRS Type 2
- Implementation of 5G NR Downlink DMRS type 2 (generation on gNB side, channel estimation with linear interpolation in frequency domain on UE side), needed for MIMO
  
MR961 : 5G NR UE TTI cleanup  
- Remove current_thread_id array, nr_tti_rx, nr_tti_tx, subframe_rx and subframe_tx

MR965 : fix a segdev

The LDPC lifting size has to be stored for each harq_process as its only assigned in the first round.