nr-UE: bugfixes
pbchsim: adding options to input/output signal files

bugfixes

adding N_RB_DL to nr_init_params, as it is needed in the gNB and the function is shared between gNB and UE. This should be revisited.

Still a remaining issue with the SNR normalization, way too low to get errors.

0. unwiring of 40 MHz channel hard-coding and general SSB location
1. PSS dynamic range improvement and DC carrier fix
2. SSS channel estimation and detection corrected
3. PBCH channel estimation fixed
4. PBCH channel extraction/compensation reworked for the general case
5. fixed-point low-complexity polar decoder integrated to PBCH decoding chain

works by default (nr_pbchsim) at 100 MHz / 30 kHz SCS and SSB wherever (but known to UE)