reading event id from EVM FED (71X backport)

Hi,
This is backport from 72X pull request #4885.

Changes/bugfixes from MWGR3:
* reading 32 bit event ID from GTP (EVM) FED. useL1EventID parameter is provided for switching back to 24-bit ID (if there are problems with runs where TCDS is used)
* added generation of this FED & event ID to Fake BU generator source
* fix for buffering code when using single input buffer in input source