PCI: rockchip: Remove pci_epf_linkup() from Rockchip EP driver

pci_epf_linkup() is intended to be invoked if the EPC supports linkup
notification. Now that pci-epf-test uses get_features callback, which
indicates Rockchip EP driver doesn't support linkup notification, remove
pci_epf_linkup() from Rockchip EP driver.

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>
Acked-by: Shawn Lin <shawn.lin@rock-chips.com>