compositor: factor out RGB shader.

Simplify RGB shader code and split off common code that could be reused.
This is preparatory work for YUV shaders.

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>
diff --git a/src/compositor.h b/src/compositor.h
index 8e3225f..533de3f 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -270,7 +270,7 @@
 	EGLContext egl_context;
 	EGLConfig egl_config;
 	GLuint fbo;
-	struct weston_shader texture_shader;
+	struct weston_shader texture_shader_rgba;
 	struct weston_shader solid_shader;
 	struct weston_shader *current_shader;
 	struct wl_display *wl_display;