realtek: dsa: rtl93xx: Configure default QoS prioritization

realtek: dsa: rtl93xx: Configure default QoS prioritization

RTL838x+RTL839x both configure a default QoS behavior with a default
mapping. This also needs to be added to RTL93xx to ensure a consistent
behavior:

* Set the default mapping between DSCP and priority: prio = dscp >> 3.
* Set the default mapping between internal priority and queues
* Set uniform prioritization of queues (as with other SoCs)

Signed-off-by: Issam Hamdi <ih@simonwunderlich.de>
Co-developed-by: Sven Eckelmann <se@simonwunderlich.de>
Signed-off-by: Sven Eckelmann <se@simonwunderlich.de>
Link: https://github.com/openwrt/openwrt/pull/20640
Signed-off-by: Robert Marko <robimarko@gmail.com>