stmmac: intel: Enable 2.5Gbps for Intel AlderLake-S

Intel AlderLake-S platform is capable of running on 2.5GBps link speed.

This patch enables 2.5Gbps link speed on AlderLake-S platform.

Signed-off-by: Wong Vee Khee <vee.khee.wong@linux.intel.com>
Link: https://lore.kernel.org/r/20220225023325.474242-1-vee.khee.wong@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>