Fix compile warnings

Author: jvandermey-evertz

src/displayapp/screens/SystemInfo.cpp

@@ -20,6 +20,8 @@ namespace {
         return "BMA421";
       case Pinetime::Controllers::MotionController::DeviceTypes::BMA425:
         return "BMA425";
+      case Pinetime::Controllers::MotionController::DeviceTypes::Unknown:
+        return "???";
     }
     return "???";
   }

src/libs/lv_conf.h

@@ -295,6 +295,7 @@ typedef void* lv_img_decoder_user_data_t;
 #define LV_TICK_CUSTOM     1
 #if LV_TICK_CUSTOM == 1
 #define LV_TICK_CUSTOM_INCLUDE  "FreeRTOS.h"       /*Header for the system time function*/
+uint32_t xTaskGetTickCount(); /*Forward declare to avoid compiler warning*/
 #define LV_TICK_CUSTOM_SYS_TIME_EXPR (xTaskGetTickCount()) /*Expression evaluating to current system time in ms*/
 #endif   /*LV_TICK_CUSTOM*/