net: Allow FIXED_PHY to be modular.

Otherwise we get things like:

warning: (NET_DSA_BCM_SF2 && BCMGENET && SYSTEMPORT) selects FIXED_PHY which has unmet direct dependencies (NETDEVICES && PHYLIB=y)

In order to make this work we have to rename fixed.c to fixed_phy.c
because the regulator drivers already have a module named "fixed.o".

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/phy/Kconfig b/drivers/net/phy/Kconfig
index b4b0f80..a3c251b 100644
--- a/drivers/net/phy/Kconfig
+++ b/drivers/net/phy/Kconfig
@@ -119,8 +119,8 @@
 	  Supports the KSZ9021, VSC8201, KS8001 PHYs.
 
 config FIXED_PHY
-	bool "Driver for MDIO Bus/PHY emulation with fixed speed/link PHYs"
-	depends on PHYLIB=y
+	tristate "Driver for MDIO Bus/PHY emulation with fixed speed/link PHYs"
+	depends on PHYLIB
 	---help---
 	  Adds the platform "fixed" MDIO Bus to cover the boards that use
 	  PHYs that are not connected to the real MDIO bus.