MFC r362736, r364088

r362736:
Configure rx_delay/tx_delay values for RK3399/RK3328 GMAC

For 1000Mb mode to work reliably TX/RX delays need to be configured
between the TX/RX clock and the respective signals on the PHY
to compensate for differing trace lengths on the PCB.

Reviewed by: manu

r364088:
Improve Rockchip's integration of if_dwc

• Do not rely on U-Boot for clocks configuration, enable and set frequencies in the driver's attach method.
• Adjust MAC settings according to detected linespeed on RK3399 and RK3328.
• Add support for RMII PHY mode on RK3328.

Reviewed by: manu
Differential Revision: https://reviews.freebsd.org/D26006