net: phy: declare package-related struct members only if CONFIG_PHY_PACKAGE is enabled

Now that we have an own config symbol for the PHY package module,
we can use it to reduce size of these structs if it isn't enabled.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://patch.msgid.link/f0daefa4-406a-4a06-a4f0-7e31309f82bc@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>