PCI: xilinx: Update Zynq binding with Microblaze node

Update Zynq PCI binding documentation with Microblaze node.

[bhelgaas: fix "microbalze_0_intc" typo]
Signed-off-by: Bharat Kumar Gogada <bharatku@xilinx.com>
Signed-off-by: Ravi Kiran Gummaluri <rgummal@xilinx.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Michal Simek <michal.simek@xilinx.com>