phy: renesas: r8a779f0-ether-serdes: add new step added to latest datasheet

R-Car S4-8 datasheet Rev.1.20 describes some additional register
settings at the end of the initialization.

Signed-off-by: Michael Dege <michael.dege@renesas.com>
Link: https://lore.kernel.org/r/20250703-renesas-serdes-update-v4-2-1db5629cac2b@renesas.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>