rdp: Improve raw surfaces

rdp: Improve raw surfaces

This patch does miscellanous improvements with raw surfaces:
* some frames markers are sent to identify a single frame made of
multiple surface updates
* we send the dirty sub-rectangles instead of the full bouncing box
* the size of the fragmentation buffer is now honored, so that our big
surface updates don't look like a DoS
* the subtile and image flipping are done in one step (not requiring a
temporary tile)
* we don't care about the size of the dirty region and always use the
preferred codec for surface update