ARM: at91: Fix link breakage when !CONFIG_PHYLIB

Fixes:
arch/arm/mach-at91/built-in.o: In function `ksz9021rn_phy_fixup':
:(.text+0x1174): undefined reference to `mdiobus_write'
:(.text+0x1188): undefined reference to `mdiobus_write'
:(.text+0x119c): undefined reference to `mdiobus_write'
:(.text+0x11b0): undefined reference to `mdiobus_write'
arch/arm/mach-at91/built-in.o: In function `sama5_dt_device_init':
:(.init.text+0x1e34): undefined reference to `phy_register_fixup_for_uid'

when CONFIG_PHYLIB is not selected.
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/mach-at91/Kconfig

@@ -163,6 +163,7 @@ config MACH_SAMA5_DT
 	bool "Atmel SAMA5 Evaluation Kits with device-tree support"
 	depends on SOC_SAMA5
 	select USE_OF
+	select PHYLIB if NETDEVICES
 	help
 	  Select this if you want to experiment device-tree with
 	  an Atmel Evaluation Kit.

arch/arm/mach-at91/board-dt-sama5.c

@@ -62,7 +62,8 @@ static int ksz9021rn_phy_fixup(struct phy_device *phy)
 
 static void __init sama5_dt_device_init(void)
 {
-	if (of_machine_is_compatible("atmel,sama5d3xcm"))
+	if (of_machine_is_compatible("atmel,sama5d3xcm") &&
+	    IS_ENABLED(CONFIG_PHYLIB))
 		phy_register_fixup_for_uid(PHY_ID_KSZ9021, MICREL_PHY_ID_MASK,
 			ksz9021rn_phy_fixup);