net: dsa: microchip: add ksz_setup_tc_mode() function

Add ksz_setup_tc_mode() to make queue scheduling and shaping
configuration more visible.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>