ibc: Don't handle HW concerns in nir_to_ibc

We'll handle things like this in a pass that lowers integer multiplication instructions as needed, per platform. Removing this check allows dEQP-VK.glsl.operator.binary_operator.mul* to pass on Skylake.

(I talked to Jason last week and we're much more interested in getting benchmarks running and getting all shaders in shader-db compiling than getting all the cases handled)