PCI: cadence: Remove pci_epf_linkup() from Cadence EP driver

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