Install ESP32_Grbl and Marlin firmware at the same time

We can install ESP32_Grbl and Marlin firmware into PandaZHU/M4 at the same time, in that case you can switch the CNC and 3D print without flash firmware each time.

download the esp32_grbl to partition app0 , and marlin firmware to partition app1 as showing in the follow picture.

the address offset for app0 is 0x10000, app1 is 0x1E0000

after download,you can switch grbl and marlin firmware with gcode M130 and then reboot