Refactor the driver to prepare for EP mode.

Add of-match data to the existing compatible, and explicitly define it as
DW_PCIE_RC_TYPE. This way, we will be able to add EP mode in a follow-up
commit in a much less intrusive way, which makes the follow-up commit much
easier to review.

No functional change intended.

Link: https://lore.kernel.org/linux-pci/20240607-rockchip-pcie-ep-v1-v5-9-0a042d6b0049@kernel.orgSigned-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>