Rtl_iofile ioformat doesn't propagate to Verilog test bench

[tjomiv]

Creating a new instance of rtl_iofile and setting the parameter ioformat to some value doesn't correctly propagate to the generated Verilog test bench.

E.g., setting the ioformat to %b

_ = rtl_iofile(self, name, ..., ioformat = '%b')

should cause the given ioformat to propagate to function rtl_io() in https://github.com/TheSystemDevelopmentKit/rtl/blob/master/rtl/sv/verilog_iofile.py, which generates the file IO operations in the Verilog test bench. Currently the default value %d is used for every file read, which causes issues with some data types.