phy: Sparx5 Eth SerDes: Use direct register operations

Use direct register operations instead of a table of register
information to lower the stack usage.
Signed-off-by: Steen Hegelund <steen.hegelund@microchip.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20210329141309.612459-2-steen.hegelund@microchip.comSigned-off-by: Vinod Koul <vkoul@kernel.org>