Let's switch the driver to using threaded IRQ so that we do not need to
manage the interrupt and work separately, and we do not acknowledge
interrupt until we finished handling it completely.

Tested-by: Adam Ford <aford173@gmail.com> #imx6q-logicpd
Tested-by: Sven Van Asbroeck <TheSven73@gmail.com> # ILI2118A variant
Tested-by: Marek Vasut <marex@denx.de> #  ILI2117
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>