PCI: rockchip: Use standard PCIe definitions

Current code uses custom-defined register offsets and bitfields for the
standard PCIe registers. This creates duplication as the PCI header already
defines them. So, switch to using the standard PCIe definitions and drop
the custom ones.

Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Geraldo Nascimento <geraldogabriel@gmail.com>
[mani: commit message rewording]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
[bhelgaas: include bitfield.h]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/e81700ef4b49f584bc8834bfb07b6d8995fc1f42.1751322015.git.geraldogabriel@gmail.com