PCI: dwc: Use DBI accessors instead of own config accessors

The Designware DBI space contains the root bus bridge config space.
Platforms needing custom {rd,wr}_own_conf functions are also the ones
needing custom {read,write}_dbi ops functions and the access sequences
are the same.

Replace all dw_pcie_{rd,wr}_own_conf() calls with the DBI variants in
preparation to remove dw_pcie_{rd,wr}_own_conf().

Link: https://lore.kernel.org/r/20200821035420.380495-3-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Jingoo Han <jingoohan1@gmail.com>
Cc: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>