Update SDK config for nRF52840 to disable UART1 instance (Mbed serial port uses UARTE peripheral)

Author: AGlass0fMilk

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/TARGET_MCU_NRF52840/config/sdk_config.h

@@ -5665,7 +5665,7 @@
 // <e> UART1_ENABLED - Enable UART1 instance
 //==========================================================
 #ifndef UART1_ENABLED
-#define UART1_ENABLED 1
+#define UART1_ENABLED 0
 #endif
 // </e>