Instead of doing if/else if/else on the chip's model number let's define
chip operations structure and use it to perform indirect calls. With number
of protocols supported by the driver growing, this makes it better
maintainable.

This change includes fixes to checks whether the driver should continue
polling the controller by Sven Van Asbroeck <thesven73@gmail.com>.

Tested-by: Adam Ford <aford173@gmail.com> #imx6q-logicpd
Tested-by: Sven Van Asbroeck <TheSven73@gmail.com> # ILI2118A variant
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>