gallium: add pipe_blit_info::dst_sample, update u_blitter to write that sample
A new radeonsi blit test will use it to upload different sample values into MSAA textures.
Due to an influx of spam, we have had to impose restrictions on new accounts. Please see this wiki page for instructions on how to get full permissions. Sorry for the inconvenience.
A new radeonsi blit test will use it to upload different sample values into MSAA textures.