libcgc: Operand register fields

These seems to be the operand register fields. It's still unknown
what type=0 means. Use D3D-style names for registers:

 * rXX = temp-register
 * vXX = input-register
 * cXX = constant-register

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>