lib/drmtest: add gpu quiescent helper

Some tests are higly timing dependent and others carelessly leave
active buffers behind. So add a helper to quiescent the gpu and call
it unconditionally when opening an fd in a vain attempt to make all
this race-condition hitting more scientifically sound.

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

lib/drmtest.h

@@ -36,6 +36,7 @@
 int drm_open_any(void);
 int drm_open_any_master(void);
 
+void gem_quiescent_gpu(int fd);
 
 void gem_set_tiling(int fd, uint32_t handle, int tiling, int stride);
 void gem_close(int fd, uint32_t handle);