net: phy: phylink: Allow specifying PHY device flags

In order to let subsystems like DSA fully utilize PHYLINK, we need to be able
to communicate phy_device::flags from of_phy_{connect,attach} even when using
PHYLINK APIs.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>