fate: make lavfi tests output only md5
Instead of saving huge raw files, use the md5: output pseudo-protocolto calculate the checksum of the file directly. This is especiallyuseful when testing on remote targets as it avoids transferring 3.6GBover the network.
Add lavfi-pixfmts LE tests.
The corresponding lavfi-pixfmts BE tests are not yet added, as thereare some bugs in the scaler (scaling rgba, argb, bgra, abgr, yuva420p)which result in differences with the LE reference, and I cannotvisually check the generated files on BE....