vrend_renderer: use GL_RGBA8UI instead of GL_RGBA8_SNORM

glTexBuffer doesn't accept GL_RGBA8_SNORM, so use GL_RGBA8UI instead. Unfortunately, we can't use our texture table since Gallium requests PIPE_FORMAT_R8_UNORM for texture buffers. For normal sampler views, the correct semantics are passed down later, but for images (where texture and image formats can differ) this is not case.

Fixes: dEQP-GLES31.functional.image_load_store.buffer.format_reinterpret.rgba8ui_rgba8_snorm dEQP-GLES31.functional.image_load_store.buffer.format_reinterpret.r32ui_rgba8_snorm dEQP-GLES31.functional.image_load_store.buffer.format_reinterpret.rgba8i_rgba8_snorm dEQP-GLES31.functional.image_load_store.buffer.format_reinterpret.rgba8_rgba8_snorm

Fixes: #11 (closed)