net: ti: icssg-prueth: Add support for half duplex operation

This patch adds support for half duplex operation at 10M and 100M link
speeds for AM654x/AM64x devices.
- Driver configures rand_seed, a random number, in DMEM HD_RAND_SEED_OFFSET
field, which will be used by firmware for Back off time calculation.
- Driver informs FW about half duplex link operation in DMEM
PORT_LINK_SPEED_OFFSET field by setting bit 7 for 10/100M HD.

Hence, the half duplex operation depends on board design the
"ti,half-duplex-capable" property has to be enabled for ICSS-G ports if HW
is capable to perform half duplex.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>