v3d/tex: handle correctly coordinates for cube/cubearrays images
When fetching for cube maps, we need to interpret them as 2d texture arrays, being the third coordinate the index for the face.
This seems that was not an issue becore all the OpenGL image storage/load tests seems to be using 0 as the base mip level.
This was detected (so needed) with the Vulkan CTS tests, as there are tests that specifically set the base level differen to zero, like these: dEQP-VK.binding_model.shader_access.primary_cmd_buf.storage_image.fragment.single_descriptor.cube_base_mip dEQP-VK.binding_model.shader_access.primary_cmd_buf.storage_image.compute.multiple_descriptor_sets.multiple_contiguous_descriptors.cube_array_base_mip