* Heltec tracker: new 'periph_power' shared pin (between Display & GPS)

variants/heltec_tracker/platformio.ini

@@ -19,7 +19,7 @@ build_flags =
   -D PIN_TFT_RST=39   ; RES 
   -D PIN_TFT_CS=38
   -D USE_PIN_TFT=1
-  -D PIN_TFT_VDD_CTL=3       ; Vext is connected to VDD which is also connected to LEDA
+  -D PIN_VEXT_EN=3       ; Vext is connected to VDD which is also connected to OLED & GPS
   -D PIN_TFT_LEDA_CTL=21     ; LEDK (switches on/off via mosfet to create the ground)
   -D PIN_GPS_RX=33
   -D PIN_GPS_TX=34