PCI: dwc: Remove Keystone specific dw_pcie_host_ops

Now that Keystone started using its own msi_irq_chip, remove
Keystone specific callback functions defined in dw_pcie_host_ops.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>