Only show the 'calibrate' sysfs attribute on chip flavours
which support calibration by writing to a calibration register.

Do this by adding a flag to the chip operations structure.
Signed-off-by: Sven Van Asbroeck <TheSven73@gmail.com>
Link: https://lore.kernel.org/r/20191112210148.3535-2-TheSven73@gmail.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>