drivers: eth: gmac: Enable 802.1Qav support
drivers: eth: gmac: Enable 802.1Qav support

This commit makes the driver enable HW Qav support for all available
priority queues.

Note that the hardware doesn't support setting the deltaBandwidth
parameter directly, but it is possible to do this by calculating it
from the negotiated link speed.

The default settings are set according to 802.1Qav 34.3.1, that says:

  The recommended default value of deltaBandwidth(N) for the highest
  numbered traffic class supported is 75%, and for any lower
  numbered traffic classes, the recommended default value is 0%.

The default/recommended values can be changed using the ethernet
management API (set_config) - which this commit also adds.

Signed-off-by: Tomasz Gorochowik <265c7c25eca9aa9127910457b0aea7e793d329f1@antmicro.com>

GiulianoFranchetto/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,kraj/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,galak/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,punitvara/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr,ldts/zephyr,punitvara/zephyr,explora26/zephyr,finikorg/zephyr,ldts/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,kraj/zephyr,galak/zephyr,kraj/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,finikorg/zephyr,explora26/zephyr,galak/zephyr,galak/zephyr,kraj/zephyr,Vudentz/zephyr,galak/zephyr,kraj/zephyr,ldts/zephyr,finikorg/zephyr