Staging: udlfb: improved rendering performance

Rework rendering for improved performance

Approx 10-20% gain avg across several "benchmarks": x11perf, gtkperf, glxgears
Moves from a single pre-alloc'd urb protected by a long-held mutex
To a list of (4) pre-alloc'd urbs which can be dispatched asynchonously

Improved rendering algorithm to hardware with lower CPU consumption,
fewer system memory accesses, and slightly higher compression.

Better scalability to multiple processors, especially with
multiple framebuffers active.

Signed-off-by: Bernie Thompson <bernie@plugable.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>