lib: add a single include header

Add a header that includes all the headers for the library. This allows
reorganisation of the library without affecting programs using it and
also simplifies the headers that need to be included to use the library.

Signed-off-by: Thomas Wood <thomas.wood@intel.com>

tests/gem_ctx_create.c

@@ -25,12 +25,11 @@
  *
  */
 
+#include "igt.h"
 #include <stdio.h>
 #include <string.h>
 #include <errno.h>
 
-#include "ioctl_wrappers.h"
-#include "drmtest.h"
 
 int ret, fd;
 struct drm_i915_gem_context_create create;