net: phy: add phy_inband_caps()

net: phy: add phy_inband_caps()

Add a method to query the PHY's in-band capabilities for a PHY
interface mode.

Where the interface mode does not have in-band capability, or the PHY
driver has not been updated to return this information, then
phy_inband_caps() should return zero. Otherwise, PHY drivers will
return a value consisting of the following flags:

LINK_INBAND_DISABLE indicates that the hardware does not support
in-band signalling, or can have in-band signalling configured via
software to be disabled.

LINK_INBAND_ENABLE indicates that the hardware will use in-band
signalling, or can have in-band signalling configured via software
to be enabled.

LINK_INBAND_BYPASS indicates that the hardware has the ability to
bypass in-band signalling when enabled after a timeout if the link
partner does not respond to its in-band signalling.

This reports the PHY capabilities for the particular interface mode,
not the current configuration.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tIUre-006ITz-KF@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>