-To avoid including the whole x2 libraries for the corresponding executables

Maybe not the right way to do.
To be checked.

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

additional 50% speed improvement with SIMD vectors

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

-Remaining LTE dependency in RLC add_srb function (not used for NSA setup)
-Rename function for DRB static preconfiguration used in noS1 mode

- this was necessary because as soon as the gNB starts, it tries detecting
  the prach preambles and it mesaures the background noise. However, there is
  a delay of several dozens of frames before it considers the preables as
  detected.
- the solution at the UE consists in avoiding sending preamble as soon as the
  UE syncs by introducing an offset, this keeps the power measurements low at
  gNB side as long as the preamble detection counter is under threshold

added longer prefix in PRACH symbol zero period for 15/30 kHz SCS. Both gNB and UE processing is modified. prachsim is functional again with new FAPI interfaces.

- RA resource selection and transmission
- MAC header structs for RA
- RA procedure msg1 fixes
- code cleanup

- Updated PRACH procedures and general code formatting
- gNB msg1 handling and RAR generation
- general bug fixing
- formatting
- missing headers
- RAR handling.

Bugfix: 1. fix the initial memory allocation; 2. correct the generation of the prach signal according to specs