gem_tiled_swapping: Limit to available memory

If there is not enough free RAM+swap for us to execute our test, we will
hit OOM, so check first.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

lib/igt_aux.h

@@ -61,6 +61,7 @@ void igt_wait_for_keypress(void);
 
 /* These are separate to allow easier testing when porting, see the comment at
  * the bottom of intel_os.c. */
+uint64_t intel_get_avail_ram_mb(void);
 uint64_t intel_get_total_ram_mb(void);
 uint64_t intel_get_total_swap_mb(void);