add Xilinx Virtex Architecture Description and DSP48E1

[vcanumalla]

This PR will be opened when the following is complete. The DSP48E1 is already in lakeroad-private, but we also need to do the following

• [x] Create new architecture description for a "vintage" xilinx virtex with DSP48E1.
  • additionally remove the other primitives like LUTs
• [x] Have new DSP yaml in the new architecture description detailing the ports and parameters of DSP48E1
• [x] Integration tests for import.