[media] v4l2-framework.txt: add SDR device type

Add SDR device type to v4l2-framework.txt document.

Cc: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: NAntti Palosaari <crope@iki.fi>
Acked-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

Documentation/video4linux/v4l2-framework.txt

@@ -768,6 +768,7 @@ types exist:
 VFL_TYPE_GRABBER: videoX for video input/output devices
 VFL_TYPE_VBI: vbiX for vertical blank data (i.e. closed captions, teletext)
 VFL_TYPE_RADIO: radioX for radio tuners
+VFL_TYPE_SDR: swradioX for Software Defined Radio tuners
 
 The last argument gives you a certain amount of control over the device
 device node number used (i.e. the X in videoX). Normally you will pass -1