Add power off command to I2cDev_PPmod class (#3152)

firmware/common/i2cdev_ppmod.hpp

@@ -59,7 +59,8 @@ class I2cDev_PPmod : public I2cDev {
         COMMAND_SHELL_PPTOMOD_DATA,       // pp shell to esp. size not defined
         COMMAND_SHELL_MODTOPP_DATA_SIZE,  // how many bytes the esp has to send to pp's shell
         COMMAND_SHELL_MODTOPP_DATA,       // the actual bytes sent by esp. 1st byte's 1st bit is the "hasmore" flag, the remaining 7 bits are the size of the data. exactly 64 byte follows.
-
+        // poweroff command
+        COMMAND_POWER_OFF,  // requests power off from the esp, and after it needs a full power cycle to get it back again
     };
 
     typedef struct {
@@ -92,6 +93,8 @@ class I2cDev_PPmod : public I2cDev {
     uint16_t get_shell_buffer_bytes();
     bool get_shell_get_buffer_data(uint8_t* buff, size_t len);
 
+    bool send_poweroff_command();  // sends the command to power off the device. Restarting the esp needs a full power cycle!
+
    private:
     uint8_t self_timer = 0;
     uint64_t mask = 0;  // feauture mask, that indicates what the device can do. this will determinate what we will query from the device