arm64: dts: exynos: correct GIC CPU interfaces address range on Exynos7

The GIC-400 CPU interfaces address range is defined as 0x2000-0x3FFF (by
ARM).

Reported-by: Sam Protsenko <semen.protsenko@linaro.org>
Reported-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Fixes: b9024cbc ("arm64: dts: Add initial device tree support for exynos7")
Link: https://lore.kernel.org/r/20210805072110.4730-1-krzysztof.kozlowski@canonical.com