OAI UE: add shared RSRP Table 10.1.6.1-1 mapping helper and adopt it RRC UE

- Add to common/utils/nr/nr_common remove from NR_MAC_UE/nr_ue_procedures.c
- Adopt in asn1_msg.c for MeasurementReport: this solves the following assert:

Assertion (enc_rval.encoded > 0) failed!
In do_nrMeasurementReport_SA() /oai-ran/openair2/RRC/NR/MESSAGES/asn1_msg.c:898
ASN1 message encoding failed (MeasResultServMOList, 18446744073709551615)!

Motivation: unify RSRP-to-index mapping across layers and fix NR RRC MeasurementReport
encoding failures due to out-of-range values by reusing the validated mapping.

Note NR_RSRP-Range.c constraint:
	{ APC_CONSTRAINED,	 7,  7,  0,  127 }	/* (0..127) */

common/utils/nr/nr_common.h

@@ -186,6 +186,9 @@ typedef struct meas_s {
   val_init_t csi_rsrp_dBm;
 } meas_t;
 
+/** @brief Returns NR RSRP index per 3GPP TS 38.133 Table 10.1.6.1-1 */
+uint8_t get_rsrp_index(int rsrp_dBm);
+
 /**
  * @brief To start a timer
  * @param timer Timer to be started