Upload speed config in boards.txt (57600 please)

[TMRh20]

I have 3 ESP32 ((WiFi Kit 32 w/OLED) modules from 2 different places, and none of them are detected in Linux, Mac or Windows devices, so I eventually discovered that I have to use a USB to TTL converter. ( Would love to solve this problem, but I digress)

I had one CP2102 based USB to TTL device laying around, so I tried it with my ESP32 and it works fine, but only at lower upload speeds such as 57600 baud. It may or may not work at 115200, but is not reliable. In order to get it working, of course I had to modify the boards.txt file to include this speed. With the DTR and RTS pins connected, it supports automated uploads too.

I'm suggesting adding 57600 baud upload speed as an option for these devices, since it would help people having trouble with certain USB->TTL units.