net: Fix sungem_phy sharing.

Since sungem_phy is used by multiple, unrelated, drivers make it
build as a real module under drivers/net.

depmod will pick up the symbol dependency and make sure sungem_phy.ko
gets loaded any time sungem.ko or spider_net.ko is loaded.

Tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>