vc4: Re-add R4 to the "any" register class.
vc4: Re-add R4 to the "any" register class.

I screwed this up in fdad4d24024ab7bc9b6b9cb6288f8b76ccac0d89 which was
supposed to be making this code more maintainable.  What's amazing is
multithreaded FS showed the wins it did despite this bug.

shader-db results:
total instructions in shared programs: 103535 -> 100548 (-2.89%)
instructions in affected programs:     83794 -> 80807 (-3.56%)

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler