PCI: keystone: Move dw_pcie_setup_rc() out of ks_pcie_establish_link()

No functional change. Move dw_pcie_setup_rc() out of
ks_pcie_establish_link() so that ks_pcie_establish_linki() can be used only
to start the link.

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