feat(boards): Add preonic_rev3 board.

app/boards/arm/preonic/Kconfig.defconfig

@@ -0,0 +1,17 @@
+# Preonic keyboard configuration
+
+# Copyright (c) 2022 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+if BOARD_PREONIC_REV3
+
+config ZMK_KEYBOARD_NAME
+    default "Preonic V3"
+
+config ZMK_USB
+    default y
+
+config ZMK_KSCAN_MATRIX_POLLING
+    default y
+
+endif # BOARD_PREONIC_REV3