PCI: rcar: Add endpoint mode support

Add support for R-Car PCIe controller to work in endpoint mode.

Link: https://lore.kernel.org/r/1588854799-13710-8-git-send-email-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>