net: phy: move __phy_package_[read|write]_mmd to phy_package.c

Move both functions to phy_package.c, so that phy_core.c no longer
has a dependency on phy_package.c (phy_package_address).

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://patch.msgid.link/8956fa53-3eda-4079-8203-a8fddcc17bf3@gmail.com


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