PCI: rzg3s-host: Use shared reset controls for power domain resets

Switch to shared reset controls for PCIe power resets to prepare for
RZ/V2H(P) support. On this platform, multiple PCIe controllers share
the same reset line, requiring shared ownership of the reset control.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Tested-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Link: https://patch.msgid.link/20260629220932.861445-3-prabhakar.mahadev-lad.rj@bp.renesas.com