Platform/Sgi: Add Iort table for RD-N2

Add Iort table specific to RD-N2 platform. RD-N2 has five PCIe root
buses and each of them are connected to an ITS node. The remapping
topology for each PCIe RC node to ITS node is shown below:

  0x0000  ---------------   0x60000   ------------
         |  PCIe device  |---------->|     ITS    |
         | (RequesterID) |           | (DeviceID) |
  0xFFFF  ---------------   0x6FFFF   ------------

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I24aa4c00e7d2ceef21fcb6803b6c68bf33bd78ba