Add the DT node for the GPU core found on the i.MX8QM.

etnaviv-gpu 53100000.gpu: model: GC7000, revision: 6009
[drm] Initialized etnaviv 1.4.0 20151214 for etnaviv on minor 0
Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>