PCI: aardvark: Convert to use pci_host_probe()

Part of advk_pcie_probe() is exactly an open-coded version of
pci_host_probe(). So instead of duplicating this code, use
pci_host_probe() directly.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>