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>

tools/intel_stepping.c

@@ -33,6 +33,7 @@
 #include <err.h>
 #include "intel_chipset.h"
 #include "intel_gpu_tools.h"
+#include "intel_reg.h"
 
 static void
 print_clock(const char *name, int clock) {