refactor(gicv3): rename GIC Clayton to GIC-700

The GIC IP formerly known as "GIC Clayton" has been released under the
name of "GIC-700".

Rename occurences of Clayton in comments and macro names to reflect the
official name.

Change-Id: Ie8c55f7da7753127d58c8382b0033c1b486f7909
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/plat/arm/board/rdn2/platform.mk b/plat/arm/board/rdn2/platform.mk
index 794f897..5b24c32 100644
--- a/plat/arm/board/rdn2/platform.mk
+++ b/plat/arm/board/rdn2/platform.mk
@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 #
 
-# RD-N2 platform uses GIC-Clayton which is based on GICv4.1
+# RD-N2 platform uses GIC-700 which is based on GICv4.1
 GIC_ENABLE_V4_EXTN	:=	1
 
 include plat/arm/css/sgi/sgi-common.mk