lib: remove uncessary #includes from headers

Only include what the header itself needs. The big fish here is
intel-gpu-tools.h. More will follow.

One ugly thing removed here is the duplicated GEN6_TD_CTL #define, one
of which was broken.

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

tests/ddi_compute_wrpll.c

@@ -4,6 +4,7 @@
 #include <stdlib.h>
 
 #include "intel_gpu_tools.h"
+#include "drmtest.h"
 
 #define LC_FREQ 2700
 #define LC_FREQ_2K (LC_FREQ * 2000)