minor clean up of the patch parametric bitfields API
minor clean up of the patch parametric bitfields API

note : this is not using traditional bit-fields as we cannot guarantee that the CPU-side
compiler will match the bit-packing of the compilers used on the GPU-side.

anshuarya/OpenSubdiv,jcowles/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,poljere/OpenSubdiv,xldeveloper/OpenSubdiv,jcowles/OpenSubdiv,c64kernal/OpenSubdiv,anshuarya/OpenSubdiv,takahito-tejima/OpenSubdiv,nyotis/OpenSubdiv,nyotis/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,poljere/OpenSubdiv,anshuarya/OpenSubdiv,takahito-tejima/OpenSubdiv,nyotis/OpenSubdiv,lookup1980/OpenSubdiv,takahito-tejima/OpenSubdiv,xldeveloper/OpenSubdiv,lookup1980/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,xldeveloper/OpenSubdiv,shengfuintel/OpenSubdiv,c64kernal/OpenSubdiv,jcowles/OpenSubdiv,c64kernal/OpenSubdiv,poljere/OpenSubdiv,lookup1980/OpenSubdiv,shengfuintel/OpenSubdiv,shengfuintel/OpenSubdiv,takahito-tejima/OpenSubdiv-exp