arm64: dts: allwinner: h5: Add device node for Mali-450 GPU

The H5 has a Mali-450 GPU with 4 Pixel Processor cores.

Interestingly, while the datasheet lists an interrupt line for the GPU's
PMU, the hardware block itself doesn't seem to have it. Reads from the
PMU address range all return zero, and writes are ignored.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>