Introduce open and close methods for the input device to keep the device
powered down when it is not in use. Also rework interaction between
interrupt thread and starting/shutting off/resetting the device: instead
of taking a mutex in the intterrupt thread and elsewhere disable interrupts
before transitioning the device in a new state.

The ESD handling is also separated from the IRQ thread; we poll regularly
at a given interval and simply skip reads if we see that valid interrupt
happened not so long ago. This allows us not cancel and reschedule ESD
work from interrupt context all the time.
Tested-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>