staging: fix more ET131X build errors

ET131X is a network device, so it should depend on
NETDEVICES.  (This part won't be needed when the driver
moves to drivers/net/.)  It also uses PHYLIB interfaces,
so it should select PHYLIB.  Fixes these build errors:

ERROR: "phy_connect" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "phy_find_first" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "mdiobus_register" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "mdiobus_alloc" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "phy_stop" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "phy_start" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "mdiobus_free" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "mdiobus_unregister" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "phy_print_status" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "phy_ethtool_gset" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "phy_ethtool_sset" [drivers/staging/et131x/et131x.ko] undefined!
ERROR: "phy_mii_ioctl" [drivers/staging/et131x/et131x.ko] undefined!

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: : Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>