i915g: Rework debug print code

src/gallium/drivers/i915/i915_screen.c

@@ -31,6 +31,7 @@
 #include "util/u_string.h"
 
 #include "i915_reg.h"
+#include "i915_debug.h"
 #include "i915_context.h"
 #include "i915_screen.h"
 #include "i915_surface.h"
@@ -330,5 +331,7 @@ i915_screen_create(struct i915_winsys *iws)
    i915_init_screen_resource_functions(is);
    i915_init_screen_surface_functions(is);
 
+   i915_debug_init(is);
+
    return &is->base;
 }