net: phy: Don't limit phy addresses by default

Some boards expect to find more than one phy while other boards are old
and need to be limited to a specific phy address. Only limit the phy
address for boards that opt in.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>