net: phy: do not force EEE support

With following patches:
commit 9b01c885 ("net: phy: c22: migrate to genphy_c45_write_eee_adv()")
commit 5827b168 ("net: phy: c45: migrate to genphy_c45_write_eee_adv()")

we set the advertisement to potentially supported values. This behavior
may introduce new regressions on systems where EEE was disabled by
default (BIOS or boot loader configuration or by other ways.)

At same time, with this patches, we would overwrite EEE advertisement
configuration made over ethtool.

To avoid this issues, we need to cache initial and ethtool advertisement
configuration and store it for later use.

Fixes: 9b01c885 ("net: phy: c22: migrate to genphy_c45_write_eee_adv()")
Fixes: 5827b168 ("net: phy: c45: migrate to genphy_c45_write_eee_adv()")
Fixes: 022c3f87 ("net: phy: add genphy_c45_ethtool_get/set_eee() support")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>