net: dsa: microchip: dcb: set default apptrust to PCP only

Before DCB support, the KSZ driver had only PCP as source of packet
priority values. To avoid regressions, make PCP only as default value.
User will need enable DSCP support manually.

This patch do not affect other KSZ8 related quirks. User will still be
warned by setting not support configurations for the port 2.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240510053828.2412516-4-o.rempel@pengutronix.de


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