Add user initiated PAT test at boot time

[pitts-mo]

Please add ability for user to initiate PAT test at boot time of normal firmwares.

Initiated by bringing SA pin high or low at boot time?

background:
I recently experienced a Whoop Lite board that appeared to have normal Red and Blue light behavior and RF output appeared normal. However, goggle was not able to receive a video signal and only occasional flashed brief flickers of green within a random signal indicator of the OSD.

[ligenxxxx]

There are many reasons why goggle cannot receive video, such as VTX RF failure or BW mismatch, damaged camera. Just outputting the colorbar does not necessarily solve the problem.