net: stmmac: move the EST structure to struct stmmac_priv

Move the EST structure to struct stmmac_priv, because the
EST configs don't look like platform config, but EST is
enabled in runtime with the settings retrieved for the TC
TAPRIO feature also in runtime. So it's better to have the
EST-data preserved in the driver private data instead of
the platform data storage.

Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Andrew Halaney <ahalaney@redhat.com>
Link: https://lore.kernel.org/r/20240513014346.1718740-3-xiaolei.wang@windriver.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>