Convert the driver to devm_request_irq(), drop the related unmanaged
deregistration code and add ili210x_irq_teardown() to tear the IRQ
down and cancel possible touchscreen pending work.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>