net: phy: bcm84881: implement phy_inband_caps() method

BCM84881 has no support for inband signalling, so this is a trivial
implementation that returns no support for inband.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/E1tIUrj-006IU6-ON@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>