net: tsec: Access eTSEC registers using virtual address

The current code accesses eTSEC registers using physical
address directly, it's not correct, though no problem on
current platforms. It won't work on platforms, which does
not support 1:1 virtual-physical address map.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>