PCI: designware: Don't complain missing *config* reg space if va_cfg0 is set

Currently on Keystone SoCs, we always complain:

  keystone-pcie 21021000.pcie: missing *config* reg space

Keystone uses an older version of DesignWare hardware that doesn't have
ATU support.  So va_cfg0_base and va_cfg1_base are already set up in
ks_dw_pcie_host_init() before calling dw_pcie_host_init(), and they point
to the remote config space address va (both same for Keystone).  Add a
check to avoid this boot noise on Keystone.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>