NR UE Rx Symbol-wise Processing

Major changes:

1. UE_thread() has been modified to read one OFDM symbol, do DFT and process the signal to generate intermediate results. At the last symbol, the remaining processing for the corresponding channel is performed.
2. nr_slot_fep() has been altered and renamed to nr_symbol_fep(). rxdata and rxdataF buffers are in stack now instead of heap. The fractional CP removal is implicitly performed while reading samples from the radio. This eliminates the need for memcpy if the starting address is not aligned.
3. Removed nr_slot_fep_init_sync(). By moving the CP removal outside of nr_symbol_fep(), there no need for special function of initial sync. So initial sync also uses nr_symbol_fep().
4. Modified PDSCH, PDCCH, PBCH, CSI & PTRS functions to accommodate the symbol based processing design. Contains both functional modifications and clean-ups.

Minor changes:

1. Clean-up DLSCH functions.
2. Using const for function inputs as much as possible.

Untested changes: CSI, PTRS and PRS modifications are not tested yet.

The following chart shows the flow of PDSCH implementation and input and output of modified functions.

new_schema_for_mr.pdf