[media] em28xx: add support for Hauppauge WinTV-dualHD DVB tuner

Hauppauge WinTV-dualHD is a USB 2.0 dual DVB-T/T2/C tuner with
following components:

USB bridge: Empia EM28274 (chip id is the same as EM28174)
Demodulator: 2x Silicon Labs Si2168-B40
Tuner: 2x Silicon Labs Si2157-A30

This patch adds support only for the first tuner.

The demodulator needs firmware, available for example here:
http://palosaari.fi/linux/v4l-dvb/firmware/Si2168/Si2168-B40/4.0.11/

The demodulators sit on the same I2C bus and their addresses
are 0x64 and 0x67. The tuners are behind the demodulators and
their addresses are 0x60 and 0x63.

Signed-off-by: Olli Salonen <olli.salonen@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>