Create a unit test for inst32 UVM object

[jerralph]

The existing instruction_unit_test.sv has testing for many different things including decoder.svh, and all the classes that were originally in instruction.svh and are now in the UVM classes for inst32, inst32_*format, where * = i,s,r,b,u,j. These classes, now in their own files, should have their own unit test file.