realtek: phy: reorganize package handling

realtek: phy: reorganize package handling

With kernel 6.18 the package shared structure will be hidden from
the phy drivers. Workaround that in advance by providing a shared
private structure that covers all information that is needed for
normal operation.

For further simplification provide a new join() function that takes
care of a consistent initialization.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/21204
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>