- the band is coming from the SI, therefore a function to get the band is not
  necessary
- this solves also the limitations of the get_band algorithm with the NR bands
  overlapping in the NR operating bands table (e.g. band 78 and band 48)

- adapted the get_band function: the algorithm is now taking into account
  also the UL frequency in order to fetch the proper band (this was failing
  before as some NR bands have the same DL band, e.g. band 65 and 66)
- added new bands to the NR table as per TS 38.101 V16.4.0 (2020)
- made the from_nrarfcn function compatible with UL FDD (this function,
  used for both DL and UL  was previously working with TDD only as it
  did not compute properly the frequency for the UL FDD, throwing asserts)
- introduced common functions to get the NR table idx and the duplex mode,
  removing repeated code in the process
- removed the unused function to get the uldl offset
- improved some logging
- other minor fixes to the relevant code

A test with band 79 was not working. It turns out that the computation
of the frequency from the NR-ARFCN was giving a wrong value.

After fixing band 79 as found in this commit, the frequency was correct.

The array nr_bandtable has then been reviewed fully and all the values
that were wrong have been changed. The check of correctness was done
using the website https://www.sqimway.com/nr_band.php

PRACH_PDU.prach_format now interpreted according to last version (March 2020) of 5G FAPI specs
fixing nr_prachsim

- Fixed random preamble selection in contention-based RA
- Cleaned-up comments and commented code

NR PHY should now be able to handle multiple PRACH occasions

  - Added support for FR1 in RO selection
  -RACH preamble selected according to the chosen RO

Check the provided MCS index according to the specified table.
Some tables go up to MCS index 27, others up to MCS index 28.
If the MCS index exceeds the allowed limit, assume max. MCS.

- To enable PTRS use -T flag followed by 3 integers
- Example: ./nr_ulsim -T 2 0 2
- 1st Value is the list of arguments -> e.g. 2
- 2nd Value is for L_PTRS{0,1,2}     -> e.g. 0
- 3rd Value is for K_PTRS{2,4}       -> e.g. 2

This commit contains work done by Eurecom and by Benetel.