realtek: 5.15: rtl93xx: support 2500baseT and 5000baseT on USXGMII links

realtek: 5.15: rtl93xx: support 2500baseT and 5000baseT on USXGMII links

The USXGMII implementation of Realtek switches can not only support
10GbE but also 2.5Gb and 5Gb on top of the usual data rates.
Mark those as supported to allow them to be negotiated.

This change has been tested on a ZyXEL XGS1250-12 with the following link
partners:
 - NWA50AX Pro (2.5Gb)
 - RTL8152 USB NIC (2.5Gb)
 - AQC111 USB NIC (2.5Gb & 5Gb)

Gbit and 10GbE has also been tested to still work fine with a variety of
devices.

Signed-off-by: Tobias Schramm <tobias@t-sys.eu>
(cherry picked from commit cd56a682326f9de4d77ee3afb99d13d25c478c08)