arm_fpga: adapt to new way of including gicv3 files
arm_fpga: adapt to new way of including gicv3 files

with commit a6ea06f5, the way platform includes gicv3 files has been
modified, this patch adapts to new method of including gicv3 files
for arm_fpga platform.

Signed-off-by: Manish Pandey <f72a68396f72e54a6338d46190da5e42d7475246@arm.com>
Change-Id: Ic5ccae842b39b7db06d4f23c5738b174c42edf63

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware