Update Zynq PCI binding documentation with Microblaze node.

[bhelgaas: fix "microbalze_0_intc" typo]
Signed-off-by: NBharat Kumar Gogada <bharatku@xilinx.com>
Signed-off-by: NRavi Kiran Gummaluri <rgummal@xilinx.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Acked-by: NRob Herring <robh@kernel.org>
Acked-by: NMichal Simek <michal.simek@xilinx.com>