Added the following structs and enums in "defs_gNB.h"
- NR_UL_gNB_HARQ_t
- NR_gNB_ULSCH_t
- NR_SCH_status_t

added the following structs in "nfapi_nr_interface.h"
- nfapi_nr_ul_config_ulsch_pdu
- nfapi_nr_ul_config_ulsch_pdu_rel15_t
- nfapi_nr_ul_srs_config_t
- nr_pusch_freq_hopping_t

added nr_ulsch.h for the ulsch decoding function declarations
- free_gNB_ulsch
- new_gNB_ulsch
- nr_ulsch_decoding

added nr_ulsch_decoding.c for the implementation of the ulsch decoding functions
- free_gNB_ulsch
- new_gNB_ulsch
- nr_ulsch_decoding