USB Serial: add a sysinfo, a radioinfo

[gullradriel]

In USB serial we would like to add two commands:

• sysinfo which would return the same stats as seen in 'Performance' when hitting DFU while on Mayhem
• radioinfo which would return the same stats as seen in 'Radio Settings' when hitting DFU a second time
• powerinfo which would return the RSSI levels and the actual power level not doable without a RSSI graph on screen, have to be an in app logging

This would allow to set a graphical view of those information in the hackrf.pp webapp, we could have one interface for each, sysinfo and powerinfo as graphs, radioinfo as a text list