Merge changes from topic "fpga_generic" into integration

* changes:
  arm_fpga: Add platform documentation
  arm_fpga: Add post-build linker script
  arm_fpga: Add ROM trampoline
  arm_fpga: Add devicetree file
  arm_fpga: Remove SPE PMU DT node if SPE is not available
  arm_fpga: Adjust GICR size in DT to match number of cores
  fdt: Add function to adjust GICv3 redistributor size
  drivers: arm: gicv3: Allow detecting number of cores