net: phylink: add phylink_expects_phy() method

[ Upstream commit 653a1809 ]

Provide phylink_expects_phy() to allow MAC drivers to check if it
is expecting a PHY to attach to. Since fixed-linked setups do not
need to attach to a PHY.

Provides a boolean value as to if the MAC should expect a PHY.
Returns true if a PHY is expected.

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Michael Sit Wei Hong <michael.wei.hong.sit@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: fe2cfbc9 ("net: stmmac: check if MAC needs to attach to a PHY")
Signed-off-by: Sasha Levin <sashal@kernel.org>