dt-bindings: net: Add documentation for Half duplex support.

In order to support half-duplex operation at 10M and 100M link speeds, the
PHY collision detection signal (COL) should be routed to ICSSG
GPIO pin (PRGx_PRU0/1_GPI10) so that firmware can detect collision signal
and apply the CSMA/CD algorithm applicable for half duplex operation. A DT
property, "ti,half-duplex-capable" is introduced for this purpose. If
board has PHY COL pin conencted to PRGx_PRU1_GPIO10, this DT property can
be added to eth node of ICSSG, MII port to support half duplex operation at
that port.

Reviewed-by: Roger Quadros <rogerq@kernel.org>
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>