ARM: realview: move DT GIC to FPGA node

ARM: realview: move DT GIC to FPGA node

This creates a node in the device tree to hold the FPGA devices
as a "simple-bus" and moves the GIC found on the FPGA to this
node, so it reflects the actual topology of the system.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>