PCI: mediatek-gen3: Configure PBUS_CSR registers for EN7581 SoC

PCI: mediatek-gen3: Configure PBUS_CSR registers for EN7581 SoC

Configure PBus base address and address mask to allow the hw
to detect if a given address is accessible on PCIe controller.

Fixes: f6ab898356dd ("PCI: mediatek-gen3: Add Airoha EN7581 support")
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/20250225-en7581-pcie-pbus-csr-v4-2-24324382424a@kernel.org
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>