lib: fold igt_display into igt_kms

For 1 function and 2 types we kinda don't need separate files.
Especially now that igt_kms is much more focused on the actual modeset
stuff with all the framebuffer helpers extracted to igt_fb.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

lib/igt_debugfs.c

@@ -33,7 +33,7 @@
 #include <unistd.h>
 
 #include "drmtest.h"
-#include "igt_display.h"
+#include "igt_kms.h"
 #include "igt_debugfs.h"
 
 /**