Feature 218 srs

this branch introduces SRS procedures in eNB. You may now enable SRS in the config file. As an example, please see config files enb.band7.tm1.usrpb210.conf and enb.band38.tm1.usrpb210.conf for FDD and TDD respectively. The configuration parameters should not be changed at this point, since the UE specific configuration will only work for the current set of cell specific parameters. This can be changed in the future. Currently the RRC will schedule SRS in a periodicity of 10ms for both TDD and FDD. This gives a support of up to 20 orthogonal SRS users in FDD and 6 in TDD config 3. Also the estimation of SRS has been included, but so far the estimation is not reported to the higher layers. Tested with TDD as well as FDD on USRPB210.