V4L/DVB (12138): em28xx: add support for Silvercrest Webcam

This webcam uses a em2710 chipset, that identifies itself as em2820,
plus a mt9v011 sensor, and a DY-301P lens.

It needs a few different initializations than a normal em28xx device.

Thanks to Hans de Goede <hdegoede@redhat.com> and Douglas Landgraf
<dougsland@redhat.com> for providing the acces for the webcam during
this weekend, I could make a patch for it while returning back from
FISL/Fudcom LATAM 2009.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/Documentation/video4linux/CARDLIST.em28xx b/Documentation/video4linux/CARDLIST.em28xx
index 873630e..014d255 100644
--- a/Documentation/video4linux/CARDLIST.em28xx
+++ b/Documentation/video4linux/CARDLIST.em28xx
@@ -66,3 +66,4 @@
  68 -> Terratec AV350                           (em2860)        [0ccd:0084]
  69 -> KWorld ATSC 315U HDTV TV Box             (em2882)        [eb1a:a313]
  70 -> Evga inDtube                             (em2882)
+ 71 -> Silvercrest Webcam 1.3mpix               (em2820/em2840)