soc: renesas: rz-sysc: Move RZ/G3S SoC detection to the SYSC driver

soc: renesas: rz-sysc: Move RZ/G3S SoC detection to the SYSC driver

Now that we have SoC detection in the RZ SYSC driver, move the RZ/G3S
SoC detection to it. The SYSC provides SoC ID in its own registers.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: John Madieu <john.madieu.xa@bp.renesas.com>
Link: https://lore.kernel.org/20250128031342.52675-3-john.madieu.xa@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>