PCI: xilinx-xdma: Add Xilinx XDMA Root Port driver

Add support for Xilinx XDMA Soft IP core as Root Port.

The Zynq UltraScale+ MPSoCs devices support XDMA soft IP module in
programmable logic.

The integrated XDMA Soft IP block has integrated bridge function that
can act as PCIe Root Port.

[kwilczynski: correct indentation and whitespaces, Kconfig help update]
Link: https://lore.kernel.org/linux-pci/20231003173453.938190-4-thippeswamy.havalige@amd.com
Signed-off-by: Thippeswamy Havalige <thippeswamy.havalige@amd.com>
Signed-off-by: Bharat Kumar Gogada <bharat.kumar.gogada@amd.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>