Signal to firmware not to load app from flash

[mchack-work]

When the firmware has the added functionality to load an app from flash in some products, the FPGA needs to have a way to indicate to the firmware that the app should be loaded in the usual way, from the client.

[mchack-work]

Decision on meeting on 2024-05-16 to try to use a touch hold for this function. See attached PR.

Needs a software test. See #223

[dehanj]

Started to investigate this, the touch sensor have a ~300 ms start up time, see attached picture. During this time the output from the touch sensor will be high, regardless of a touch or not. It seems to go low when it is ready.
This is most likely some power up sequence the touch IC needs, maybe calibration, maybe something else.

On top of this, the sensor is not registering a touch that started before the end of these 300 ms, meaning holding on the touch area and powering up the device, will not register a touch. The touch needs to start when the touch IC is ready.