UE directory splits, creation of UE-specific files, common UE/eNB files and extraction of UE/common components from eNodeB files. renaming of files to minimize common names across directories (i.e. defs.h, vars.h, extern.h)

- fix compilation of dlsim/ulsim/oaisim by defining some needed
  global variables
- fix compilation of oaisim: compile coding and params_libconfig
- fix running of if4p5 with low CPU count (oaisim was not working
  on the machine 'haswell' because of this)

This work is based on work by NTT.

To use the code, do:
./build_oai --oaisim --ue-nas-use-tun -t ETHERNET -c

This commit only handles oaisim in S1 mode.

We won't handle noS1 mode.

Only ulsim and dlsim compile. The others (dlsim_tm4 pucchsim prachsim
pdcchsim pbchsim mbmssim) have been disabled.

Command line to compile: ./build_oai --phy_simulators

The following was not working properly:

    ./build_oai -I -w USRP

After this commit it works.

And so does:

  ./build_oai --eNB -w USRP

The following did not work before this commit
on ubuntu 17.10:

    ./build_oai --oaisim -c

oaisim has not been tested. It may fail to work. To be tested.

Not sure that the use of __KERNEL__ is the correct solution.
To be checked at some point.

After this commit, the following works:
./build_oai --UE -c

removed NFAPI libraries from oaisim target. added #define to allow ue_ip.ko to compile. This should be revisited, there's a problem in CMakelists.txt, no flags.cmake generate for all 3 kernel modules.

'_' is not a valid character.

S1AP specs say:

    ENBname ::= PrintableString (SIZE (1..150,...))

And X.680 (08/2015) 41.4 table 10 lists the valid characters for
PrintableString. '_' is not there. We replace by '-' which is there.

Connection of eNB to ppenair-cn has not been tested. There is no reason
why it would fail.

all the FlexRAN scheduling code is now also handled by the general OAI
scheduling code

fixes after merge with develop. Partial UE/eNB separation in build to avoid problems with NFAPI in oaisim UE/RRU.
tested with simulator.