PCI: rockchip: Populate ->get_features() dw_pcie_ep_ops

Populate ->get_features() dw_pcie_ep_ops to return the EPC features
supported by Rockchip PCIe endpoint controller.

Tested-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>