fix(boards): Fix nRF5340 DK issues

- Fixed a stack overflow when enabling Bluetooth.
- Increased the I2C buffer size to support displays.

app/boards/nrf5340dk_nrf5340_cpuapp.overlay

@@ -0,0 +1,10 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+&arduino_i2c {
+    // Default buffer size is too small for use with displays.
+    zephyr,concat-buf-size = <512>;
+};