net: bcmgenet: Indicate MAC is in charge of PHY PM

Avoid the PHY library call unnecessarily into the suspend/resume functions by
setting phydev->mac_managed_pm to true. The GENET driver essentially does
exactly what mdio_bus_phy_resume() does by calling phy_init_hw() plus
phy_resume().

Fixes: fba863b8

 ("net: phy: make PHY PM ops a no-op if MAC driver manages PHY PM")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20220804173605.1266574-1-f.fainelli@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>