dt-bindings: PCI: dwc: Add reg/reg-names common properties

dt-bindings: PCI: dwc: Add reg/reg-names common properties

Even though there is a more-or-less limited set of the CSR spaces can be
defined for each DW PCIe controller the generic DT-schema currently
doesn't specify much limitations on the reg-space names used for one or
another range. In order to prevent the vendor-specific controller schemas
further deviation from the generic interface let's fix that by introducing
the reg-names definition in the common DW PCIe DT-schemas and preserving
the generic "reg" and "reg-names" properties in there. New DW PCIe device
DT-bindings are encouraged to use the generic set of the CSR spaces
defined in the generic DW PCIe RP/EP DT-bindings, while the already
available vendor-specific DT-bindings can still apple the common
DT-schemas.

Note the number of reg/reg-names items need to be changed in the DW PCIe
EP DT-schema since aside with the "dbi" CSRs space these arrays can have
"dbi2", "addr_space", "atu", etc ranges.

Also note since there are DW PCIe-based vendor-specific DT-bindings with
the custom names assigned to the same CSR resources we have no much choice
but to add them to the generic DT-schemas in order to have the schemas
being applicable for such devices. These names are marked as
vendor-specific and should be avoided being used in new bindings in favor
of the generic names.

Link: https://lore.kernel.org/r/20221113191301.5526-11-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>