Right now neither `sat` nor `sim` have support for the `$check` cell.
For formal verification it is a good idea to always run either
async2sync or clk2fflogic which will (in a future commit) lower `$check`
to `$assert`, etc.
While `sim` should eventually support `$check` directly, using
`async2sync` is ok for the current tests that use `sim`, so this commit
also runs `async2sync` before running sim on designs containing
assertions.
* xilinx: eliminate SCCs from DSP48E1 model
* xilinx: add SCC test for DSP48E1
* Update techlibs/xilinx/cells_sim.v
* xilinx: Gate DSP48E1 being a whitebox behind ALLOW_WHITEBOX_DSP48E1
Have a test that checks it works through ABC9 when enabled