lib: extract igt_aux.[hc]

And shovel all the various helpers in there.

Also move igt_set_vt_graphics_mode to igt_kms.h since the function is
implemented in igt_kms.c. And it fits better. I kinda missed this in
the prep work.

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

tests/eviction_common.c

@@ -30,6 +30,7 @@
 #include <stdlib.h>
 
 #include "drmtest.h"
+#include "igt_aux.h"
 
 struct igt_eviction_test_ops
 {