The simulators have been changed: due to linker errors that would arise
otherwise, a lot of functions are defined in them to avoid such errors.
Some functions are also defined in header files; in this commit, we
define most functoins in nr_dummy_functions.c, which is compiled in, not
by including the C file, but by adding it to the target in
CMakeLists.txt

- nr_dlsim+nr_ulsim need NR_IF_Module_init(), so it cannot be in
  nr_dummy_functions, but the others need it
- Link correcr NR_IF_Module_init() into these simulators, and reduce
  overall link list
- Correctly link remaining simulators

removed gNB_id and slot from function calls where proc is used.

This commit contains work done by Eurecom and by Benetel.

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.