Modifying NRPC RDO

A modification to the NRPC RDO variable names and access function naming is introduced. Reason is that the NRPC (BIS 7/8) will have a tdc board in run-3, but this will change in phase-2 when a new readout board (with no tdc) will be used. In order to keep the RDO valid for phase-2 tdc has to be replaced with board in NRPC RDO's and in all related classes. No change is applied to the actual RDO content and size.

cc @mnegrini