Conflicts when cell name equals its cell type

[acomodi]

In the process of testing a very basic LiteX design, I stumbled upon an issue for which, if a cell is given the name equal to the corresponding cell_type, than the cell would not be present in the physical netlist. E.g.:

PLLE2_ADV #( 
    <attrs>
) PLLE2_ADV (
    <ports>
);

The above does not end up in the output physical netlist.

I have tracked down the issue potentially being in the collision of cell name and cell type when checking whether to create a leaf cell or generate a submodules in nextpnr, and all the missing cells do indeed have the colliding name - type strings.

Unclear what the best solution is at the moment, but maybe we may address this when generating the logical netlist and, in case the cell name and cell type are equal, the cell name should be prefixed/suffixed with something to differentiate them.

[gatecat]

Missed this issue, but hit this myself testing LiteX stuff (#54) and have fixed it in YosysHQ/nextpnr#779