amd-xgbe: Configure and retrieve 'tx-usecs' for Tx coalescing

Ethtool has advanced with additional configurable options, but the
current driver does not support tx-usecs configuration using Ethtool.

Add support to configure and retrieve 'tx-usecs' using ethtool, which
specifies the wait time before servicing an interrupt for Tx coalescing.

Signed-off-by: Vishal Badole <Vishal.Badole@amd.com>
Acked-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Link: https://patch.msgid.link/20250816141941.126054-1-Vishal.Badole@amd.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>