net: phy: mv88e61xx: Finish migration of MV88E61XX_FIXED_PORTS

Set the default for MV88E61XX_FIXED_PORTS to 0x0 in Kconfig, and move
the comment from code to the help to explain what this does.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
diff --git a/drivers/net/phy/Kconfig b/drivers/net/phy/Kconfig
index 580ac8e..5eaff05 100644
--- a/drivers/net/phy/Kconfig
+++ b/drivers/net/phy/Kconfig
@@ -62,6 +62,10 @@
 
 config MV88E61XX_FIXED_PORTS
 	hex "Bitmask of PHYless serdes Ports"
+	default 0x0
+	help
+	  These are ports without PHYs that may be wired directly to other
+	  serdes interfaces
 
 endif # MV88E61XX_SWITCH