verilog: add memref.load, func.call and arithmetic index ops support to emitter

[copybara-service[bot]]

verilog: add memref.load, func.call and arithmetic index ops support to emitter

This adds support for function calls in the generic body as separate verilog submodules, and support for variable index load/stores (so we can support tosa::table ops!).

Note: this also updates yosys-optimizer to handle the function calls. I found out that splitnets -ports generic_body %n can split the output ports of all BUT generic_body (that's what %n does to a selection).