glupload: Implement direct dmabuf uploader

glupload: Implement direct dmabuf uploader

The idea is that some GPUs (like the Vivante series) can actually
perform the YUV->RGB conversion internally, so no custom conversion
shaders are needed. To make use of this feature, we need an additional
uploader that can import DMABUF FDs and also directly pass the pixel
format, relying on the GPU to do the conversion.

Based on patches from Nicolas Dufresne <nicolas.dufresne@collabora.com> and
Carlos Rafael Giani <dv@pseudoterminal.org>.

https://bugzilla.gnome.org/show_bug.cgi?id=783521