Integrate PiKVM-like functionality (video capture, USB gadget)

[macpijan]

Many of the RTE and PiKVM features are common.

The RTE does some more (OC GPIOs, SPI flashing, relay), and PiKVM does some more (mainly USB gadget and HDMI capture).

By integrating the most important features of PiKVM into RTE, we could simplify most setups by having a single device.

USB gadget for HID/MSC emulation should be feasible, possibly on the existing board even (Orange Pi Zero).

Video capture would need additional hw interace, however. In case of RPI, CSI camera input is used along with the HDMI - CSI bridge. Another requirement would be a hw acceleration of vide encoding - in case of PiKVM ustreamer is used which supports RPi video encoder.