arm64: dts: hisilicon: Add Mali-450 MP4 GPU DT entry

hi6220 has a Mali450 MP4 so lets add it into the DT.

Cc: Wei Xu <xuwei5@hisilicon.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: devicetree@vger.kernel.org
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>