* io_pins: implement efiSetPadUnused
When pin becomes unused it should be switched to safe mode and
disconnected from any IP block. Assume that gpio input mode with
pull-up is safe enough.
* trigger_input: switch triggers pins to safe mode on stop/reinit
* digital_input_exti: rework
* rename enableExti to efiExtiEnablePin
* add efiExtiDisablePin
* keep track of used exti channels
* trigger_input: use digital_input_exti functions