Add XIAO Wio-SX1262 overlay; support SX12xx bandwidths (including 62.5 kHz) as default

- boards/seeed/xiao_wio_sx1262: add overlay, .conf, board.yml
- app: support full set of SX12xx bandwidths; default BW set to 62 (62.5 kHz)
- Update Kconfig and prj.conf
- Update lora_modem.h/c for validation and mapping

build/CMakeFiles/clean_additional.cmake

@@ -0,0 +1,8 @@
+# Additional clean files
+cmake_minimum_required(VERSION 3.16)
+
+if("${CONFIG}" STREQUAL "" OR "${CONFIG}" STREQUAL "")
+  file(REMOVE_RECURSE
+  "zephyr/include/generated/zephyr/syscalls"
+  )
+endif()