ICSHWI-13063: Implement a PV for LLRF state machine Set Point as mbbo

Changes were made to the LLRF State Machine state selection mechanism. previously the OPI put a new state to a string out type PV. However, when using PVA we are seeing some issues with the string PVs. To solve this issue a change was made by providing a state selection mechanism that set the state as a numeric value using the mbbo type PV.