V4L/DVB (6545): em28xx: autodetect Cinergy 200 USB and VGear PocketTV

Adds autodetection support for the Cinergy200 USB and the VGear PocketTV.

Whenever a usb device with generic empia em2800 usb ids is detected the device
gets scanned for connected i2c devices. If the device list matches an em2800
device in the device list the model id gets changed accordingly.

Signed-off-by: Sascha Sommer <saschasommer@freenet.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>