[media] ASoC: WL1273 FM radio: Access I2C IO functions through pointers

These changes are needed to keep up with the changes in the
MFD core and V4L2 parts of the wl1273 FM radio driver.

Use function pointers instead of exported functions for I2C IO.
Also move all preprocessor constants from the wl1273.h to
include/linux/mfd/wl1273-core.h.

Also update the year in the copyright statement.

Signed-off-by: Matti J. Aaltonen <matti.j.aaltonen@nokia.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>