dt-bindings: PCI: qcom: Specify reg-names explicitly

Instead of specifying the enum of possible reg-names, specify them
explicitly. This allows us to specify which chipsets need the "atu"
regions and which do not. Also it clearly describes which platforms
enumerate PCIe cores using the dbi region and which use parf region for
that.

Link: https://lore.kernel.org/r/20220506152107.1527552-4-dmitry.baryshkov@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>