media: cx231xx: Add support for Hauppauge HVR-975

Hauppauge HVR-975 is hybrid NTSC/PAL, QAM/ATSC, and DVB-C/T/T2 usb device.

Only ATSC/QAM front end is initially active. Second frontend support is
work in progress.

CX23102 + LG3306A/Si2168(WiP) + Si2157

Changes since v1:
- removed double semicolon

Signed-off-by: Brad Love <brad@nextdimension.cc>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>