Testfloat vector generation refactoring + root Makefile cleanup

Created by: jordancarlin

Root Makefile

• Use standard recursive make syntax
• Add PHONY targets
• Update all rule to allow for parallel execution (depends on further changes to sim & riscof makefiles)

Testfloat Vector generation

• Use Makefiles instead of bash scripts to generate vectors
  • Allows for parallel execution (15x speedup in vector generation, 3x overall speedup)
  • Ensures proper dependencies are met
    • SoftFloat before TestFloat before vectors before
    • combined_IF_vectors will only be attempted if riscof has been completed
• Remove compiled SoftFloat binary