Default button polarity to active-LOW across all firmware types

Nearly all LoRa boards use a boot button that pulls to ground when
pressed.

variants/t1000-e/T1000eBoard.h

@@ -78,14 +78,14 @@ public:
     digitalWrite(LED_PIN, HIGH);
     #endif
     #ifdef BUTTON_PIN
-    while(digitalRead(BUTTON_PIN));
+    while(digitalRead(BUTTON_PIN) == LOW);
     #endif
     #ifdef LED_PIN
     digitalWrite(LED_PIN, LOW);
     #endif
 
     #ifdef BUTTON_PIN
-    nrf_gpio_cfg_sense_input(BUTTON_PIN, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_HIGH);
+    nrf_gpio_cfg_sense_input(BUTTON_PIN, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_LOW);
     #endif
 
     sd_power_system_off();