[kconfig]优化 PHY_USING_LAN8720A

bsp/stm32/stm32f407-atk-explorer/board/Kconfig

@@ -50,7 +50,6 @@ menu "Onboard Peripheral Drivers"
         bool "Enable Ethernet"
         default n
         select RT_USING_LWIP
-        select PHY_USING_LAN8720A
         select RT_LWIP_USING_HW_CHECKSUM
 
     config BSP_USING_ETH_SAL
@@ -60,6 +59,11 @@ menu "Onboard Peripheral Drivers"
         select RT_USING_SAL
         select SAL_USING_POSIX
 
+	config PHY_USING_LAN8720A
+		bool
+		depends on BSP_USING_ETH
+		default y
+
     config BSP_USING_MPU6050
         bool "Enable MPU6050 (i2c1)"
         default n