[media] sp2: Add I2C driver for CIMaX SP2 common interface module

Driver for the CIMaX SP2 common interface chip. It is very much based on
the existing cimax2 driver for cx23885, but should be more reusable. The
product has been sold with name Atmel T90FJR as well and the data sheets
for that chip seem to be publicly available.

It seems that the USB device that I have and the cx23885 based devices will
need to interact differently with the chip for the CAM operations. Thus
there is one callback function that is passed on to the sp2 driver
(see function sp2_ci_op_cam for that one).

IRQ functionality is not included currently (not needed by USB devices
and I don't have a PCIe device for development).

Signed-off-by: Olli Salonen <olli.salonen@iki.fi>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>