media: video-i2c: add hwmon support for amg88xx

AMG88xx has an on-board thermistor which is used for more accurate
processing of its temperature readings from the 8x8 thermopile array

Cc: linux-hwmon@vger.kernel.org
Signed-off-by: Matt Ranostay <matt.ranostay@konsulko.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>