Raise error for convolutions with unsupported types.
Raise error for convolutions with unsupported types.

The main motivation is to give a better error when FP8 convolutions are run on unsupported GPUs, but this change also raises an error on convolutions with complex types, which aren't supported on any GPU. Before this change, convolutions with unsupported types would give cryptic errors during autotuning.

Among integer convolutions, only S8 convolutions are supported. The pass CudnnFusedConvRewriter may rewrite convolutions on wider types into S8 convolutions if the inputs are casted from S8. CudnnFusedConvRewriter itself already raises an error if there are convolutions on non-S8 integral types, so there is no need to raise an error explicitly.
