PCI: dwc: Fix EP link notification implementation

Move specific features settings from EP shared code
(pcie-designware-ep.c) to the driver (pcie-designware-plat.c).

Previous implementation disables the EP link notification
by default for all SoCs that uses EP DesignWare IP, which affects
directly the dra7xx and artpec6 SoCs.

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