Rv32ud tests (#108)

* Probably implemented the changes required to support fadd test for rv32ud

* Created test files in rv32ud, implemented working(?) test for ldst

* fclass, fcvt_w, fmin and recoding seem to be working now

* Got fdiv (and sqrt) tests working

* fmadd tests seem to work

* fcmp works

* [WIP] fcvt working, but lacks a 32-bit implementation of the final test

* Renamed macro TEST_LDST_D32 to TEST_CASE_D32 to indicate that it can be used for more than just LDST

* Added Makefrag for rv32ud tests and included in main isa Makefile

* Don't run 64-bit tests if the defined XLEN is 32