exa: fix missing include of dix-config.h

This header needs to be included first, otherwise things can easily get really
messed up. The current code only works by accident, because some other header
already including it early enough - but a subtle change in include order
can easy break it.

Thus, always make sure the header is really included first.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

exa/exa_offscreen.c

@@ -25,6 +25,7 @@
  * When allocating, the contiguous block of areas with the minimum eviction
  * cost is found and evicted in order to make room for the new allocation.
  */
+#include <dix-config.h>
 
 #include "exa_priv.h"
 

exa/exa_unaccel.c

@@ -20,6 +20,7 @@
  * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
  * PERFORMANCE OF THIS SOFTWARE.
  */
+#include <dix-config.h>
 
 #include "exa_priv.h"