i965: Combine {VS,FS}_OPCODE_GET_BUFFER_SIZE opcodes.

These are the same, we don't need a separate opcode enum per backend.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/intel/compiler/brw_vec4.cpp

@@ -361,7 +361,7 @@ vec4_visitor::implied_mrf_writes(vec4_instruction *inst)
    case SHADER_OPCODE_TG4:
    case SHADER_OPCODE_TG4_OFFSET:
    case SHADER_OPCODE_SAMPLEINFO:
-   case VS_OPCODE_GET_BUFFER_SIZE:
+   case SHADER_OPCODE_GET_BUFFER_SIZE:
       return inst->header_size;
    default:
       unreachable("not reached");