gldownload: download RGB, BGR and BGRA with dmabuf

Allow these formats to be downloaded using ION backed dmabufs,
which is orders of magnitude faster than PBO transfers.

This change depends on an updated imx-gpu-viv and allows for GPU
based conversions from YUV (camera, VPU) to inference friendly
RGB (not RGBA) at the native source rate (30 fps).

Change-Id: I04c3ca9261d9ba911dff14c0df9b996637b481fb
1 file changed