soc: renesas: rz-sysc: Add syscon/regmap support

soc: renesas: rz-sysc: Add syscon/regmap support

The RZ/G3E system controller has various registers that control or report
some properties specific to individual IPs. The regmap is registered as a
syscon device to allow these IP drivers to access the registers through the
regmap API.

As other RZ SoCs might have custom read/write callbacks or max-offsets,
register a custom regmap configuration.

[claudiu.beznea:
 - do not check the match->data validity in rz_sysc_probe() as it is
   always valid
 - dinamically allocate regmap_cfg]

Signed-off-by: John Madieu <john.madieu.xa@bp.renesas.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Tested-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com> # on RZ/G3S
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20250818162859.9661-2-john.madieu.xa@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>