Add missing ASAP7 OA Verilog cell models

[taktoa]

For some reason the asap7sc7p5t_OA_RVT_TT_201020.v file was the only one missing from the set of Verilog standard cell models in flow/platforms/asap7/verilog/stdcell. ORFS does generate netlists that contain these cells, so I'm not sure how simulation could have been working previously.

[taktoa]

I see now that there is no simulation flow in ORFS currently (for some reason I thought there was a power simulation flow that made use of these models). I would recommend either completing the set here, or deleting them entirely since they seem to be unused.