v4l2: Make use of the VIDIOC_ENUM_FRAMESIZES ioctl on OpenBSD

Make use of the V4L2 VIDIOC_ENUM_FRAMESIZES ioctl on OpenBSD.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -4967,6 +4967,7 @@ check_header linux/videodev2.h
 check_code cc linux/videodev2.h "struct v4l2_frmsizeenum vfse; vfse.discrete.width = 0;" && enable_safe struct_v4l2_frmivalenum_discrete
 
 check_header sys/videoio.h
+check_code cc sys/videoio.h "struct v4l2_frmsizeenum vfse; vfse.discrete.width = 0;" && enable_safe struct_v4l2_frmivalenum_discrete
 
 check_func_headers "windows.h vfw.h" capCreateCaptureWindow "$vfwcap_indev_extralibs"
 # check that WM_CAP_DRIVER_CONNECT is defined to the proper value