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

boards/seeed/xiao_wio_sx1262/board.yml

@@ -0,0 +1,11 @@
+board:
+  name: xiao_wio_sx1262
+  full_name: "Seeed XIAO ESP32-S3 + Wio-SX1262"
+  vendor: seeed
+  socs:
+    - name: esp32s3
+      variants:
+        - name: procpu
+          cpucluster: procpu
+        - name: appcpu
+          cpucluster: appcpu