cogl: Remove poll renderer

As it is only composed of idle callbacks now, replace
those functions where they are used

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3887>

src/backends/native/meta-kms-impl-device.c

@@ -23,6 +23,7 @@
 #include <fcntl.h>
 #include <glib/gstdio.h>
 #include <linux/dma-buf.h>
+#include <poll.h>
 #include <sys/ioctl.h>
 #include <sys/timerfd.h>
 #include <xf86drm.h>