perf/arm-cc*: Fix MODULE_LICENSE() tags

The CCI/CCN drivers are licensed under GPLv2, but the MODULE_LICENSE()
tags are using the bare "GPL" string implying GPLv2 or later. Fix them
to match their actual file license.

Acked-by: Pawel Moll <pawel.moll@arm.com>
Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>