gl_shader_gen: Refactor lighting config to match Pica register naming.

- Also implement D0 LUT enable.

src/video_core/pica.h

@@ -718,6 +718,8 @@ struct Regs {
         };
 
         union {
+            BitField<16, 1, u32> lut_enable_d0; // 0: GL_TRUE, 1: GL_FALSE
+
             // Each bit specifies whether distance attenuation should be applied for the
             // corresponding light