Cleanup in r600_blit
Cleanup in r600_blit

 - Don't bother to assign vb until we know we have enough space
 - Add variables for sx2, sy2, dx2, dy2 so that these aren't
   calculated over and over, also reduce chance of errors.
 - Use switch to assign color/format

MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase