dt-bindings: gpu: mali-bifrost: Add Mediatek MT8183

Define a compatible string for the Mali Bifrost GPU found in
Mediatek's MT8183 SoCs.

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210421132841.v13.1.Ie74d3355761aab202d4825ac6f66d990bba0130e@changeid