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/rak/rak_wismesh_pocket/board.yml

@@ -2,6 +2,5 @@ board:
   name: rak_wismesh_pocket
   full_name: "RAK WisMesh Pocket"
   vendor: rak
-  url: https://docs.rakwireless.com/Product-Categories/WisMesh/
   socs:
     - name: nrf52840

boards/rak/rak_wismesh_tag/board.yml

@@ -2,6 +2,5 @@ board:
   name: rak_wismesh_tag
   full_name: "RAK WisMesh Tag"
   vendor: rak
-  url: https://docs.rakwireless.com/Product-Categories/WisMesh/
   socs:
     - name: nrf52840