Looks like we can have the maxtouch touchscreen stop producing interrupts
if an edge interrupt is lost. This can happen easily when the SoC idles as
the gpio controller may not see any state for an edge interrupt if it
is briefly triggered when the system is idle.
Also it looks like maxtouch stops sending any further interrupts if the
interrupt is not handled. And we do have several cases of maxtouch already
configured with a level interrupt, so let's do that.
With level interrupt the gpio controller has the interrupt state visible
after idle. Note that eventually we will probably also be using the
Linux generic wakeirq configured for the controller, but that cannot be
done until the maxtouch driver supports runtime PM.