net: dsa: lan9303: imply SMSC_PHY

Both LAN9303 and LAN9354 have internal PHYs on both external ports.
Therefore a configuration without SMSC PHY support is non-practical at
least and leads to:

LAN9303_MDIO 8000f00.mdio:00: Found LAN9303 rev. 1
mdio_bus 8000f00.mdio:00: deferred probe pending: (reason unknown)
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20240528073147.3604083-1-alexander.sverdlin@siemens.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/Kconfig

@@ -102,6 +102,7 @@ config NET_DSA_SMSC_LAN9303
 	tristate
 	select NET_DSA_TAG_LAN9303
 	select REGMAP
+	imply SMSC_PHY
 	help
 	  This enables support for the Microchip LAN9303/LAN9354 3 port ethernet
 	  switch chips.