motion has both v4l1 and v4l2 support but they are not separate except in upstream version control.
so, temporarily use the libv4l1-videodev.h from libv4l to allow succesful build of the v4l2 (pay attention here!) backend.

--- motion.h
+++ motion.h
@@ -40,7 +40,7 @@
 
 #define _LINUX_TIME_H 1
 #if !defined(WITHOUT_V4L) && !defined(BSD)
-#include <linux/videodev.h>
+#include <libv4l1-videodev.h>
 #endif
 
 #include <pthread.h>
--- track.c
+++ track.c
@@ -11,6 +11,7 @@
 #include "motion.h"
 
 #ifndef WITHOUT_V4L
+#include <linux/videodev2.h>
 #include "pwc-ioctl.h"
 #endif
 
--- video.h
+++ video.h
@@ -12,7 +12,7 @@
 
 #define _LINUX_TIME_H 1
 #ifndef WITHOUT_V4L
-#include <linux/videodev.h>
+#include <libv4l1-videodev.h>
 #include <sys/mman.h>
 #include "pwc-ioctl.h"
 #endif