wifi: winc1500: Rename CONFIG_WIFI_WINC1500 to CONFIG_ATMEL_WINC1500 in nm_bsp_internal.h

Rename the configuration symbol in `nm_bsp_internal.h` from CONFIG_WIFI_WINC1500
to CONFIG_ATMEL_WINC1500 to decouple the BSP header inclusion from the default
Zephyr driver.

This change allows alternative driver implementations to use the BSP headers
without being forced to enable CONFIG_WIFI_WINC1500, which otherwise enables
the built-in Zephyr driver and can cause conflicts when providing a custom
driver.

Author: lromeraj

asf/common/components/wifi/winc1500/bsp/include/nm_bsp_internal.h

@@ -7,7 +7,7 @@
 #ifndef _NM_BSP_INTERNAL_H_
 #define _NM_BSP_INTERNAL_H_
 
-#if defined(CONFIG_WIFI_WINC1500)
+#if defined(CONFIG_ATMEL_WINC1500)
 #include <wifi_winc1500_nm_bsp_internal.h>
 #endif /* CONFIG_WIFI_WINC1500 */