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>