PCI: amd-mdb: Add AMD MDB Root Port driver

PCI: amd-mdb: Add AMD MDB Root Port driver

Add support for AMD MDB (Multimedia DMA Bridge) IP core as Root Port.

The Versal2 devices include MDB Module. The integrated block for MDB
along with the integrated bridge can function as PCIe Root Port
controller at Gen5 32-GT/s operation per lane.

Bridge supports error and INTx interrupts and are handled using platform
specific interrupt line in Versal2.

Signed-off-by: Thippeswamy Havalige <thippeswamy.havalige@amd.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20250228093351.923615-4-thippeswamy.havalige@amd.com
[bhelgaas: only present on ARM64-based SoCs; squash Kconfig dependency on
ARM64 from Geert Uytterhoeven <geert+renesas@glider.be>:
https://lore.kernel.org/r/eaef1dea7edcf146aa377d5e5c5c85a76ff56bae.1742306383.git.geert+renesas@glider.be]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
[kwilczynski: commit log, code comments and error messages clean-up,
drop redundant "depends on PCI" from Kconfig, expose the error code
as part of error messages where appropriatie, change "depends on"
expression to match existing style from other drivers]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>