feat(fvp): add GICv5 support

Factors out GICv3 specific code and replace it with GICv5. This can be
selected with FVP_USE_GIC_DRIVER=FVP_GICV5. Specifically, the FCONF
logic does not apply to GICv5 as the bindings are completely different.

This patch does not include a device tree. This will be added at a later
date.

Change-Id: Ifd0c7b4e0bc2ea1e53a6779ab4c50c4aec39dafb
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
diff --git a/docs/plat/arm/fvp/fvp-build-options.rst b/docs/plat/arm/fvp/fvp-build-options.rst
index 8edcdb7..3d87494 100644
--- a/docs/plat/arm/fvp/fvp-build-options.rst
+++ b/docs/plat/arm/fvp/fvp-build-options.rst
@@ -27,6 +27,7 @@
 
    -  ``FVP_GICV2`` : The GICv2 only driver is selected
    -  ``FVP_GICV3`` : The GICv3 only driver is selected (default option)
+   -  ``FVP_GICV5`` : The GICv5 only driver is selected
 
 -  ``FVP_HW_CONFIG_DTS`` : Specify the path to the DTS file to be compiled
    to DTB and packaged in FIP as the HW_CONFIG. See :ref:`Firmware Design` for