Add xpcs_create_mdiodev() to simplify the creation of the mdio device
associated with the XPCS. In order to allow xpcs_destroy() to clean
this up, we need to arrange for xpcs_create() to take a refcount on
the mdiodev, and xpcs_destroy() to put it.
Adding the refcounting to xpcs_create()..xpcs_destroy() will be
transparent to existing users of these interfaces.
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
9a5d500cff