prepare for noS1 Issue346 targetredef

prepare for noS1 as config option and further target redefinitions as defined in May 2018 workshop. introduce a lte-softmodem-common.c to prevent duplicated code in lte-softmodem.c and lte-uesoftmodem.c. Cleanup in softmodem command line options, introduction of an API (get_softmodem_params() )for a module to get parameters entered in command line, avoiding global variables usage. Introduce a --noS1 command line option, (not yet tested), and start setting pdcp init and run-time options accordingly, some pdcp_fifo.c cleanup.