PCI: designware-ep: Do not disable BARs during initialization

Some platforms like K2G has reserved use of BAR_0 which shouldn't be
disabled by software. Avoid disabling all BARs during initialization.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>