Allow direct DMABuf upload into external-oes textures.

For hardware that contains native YUV samplers, some drivers may only support external-oes import of YUV textures.

Note that if the colorspace conversion capabilities are limited (for example Vivante GC2000 only supports conversion from BT.601 limited range natively), the EGL API does not provide any feedback on whether the YUV encoding matrix and quantization range that were requested via hints are supported. In scenarios with controlled source material, this may still be desirable for memory bandwidth savings.