radeonsi: Implement DMA blit

radeonsi: Implement DMA blit

This code is a slightly modified version of evergreen_dma_blit (and
evergreen_dma_copy as well as evergreen_dma_copy_tile).
It would be nice to share some of the code in the long term.

I have reused some "cik"-prefixed functions that also return the right
value for SI. I am not sure if they should be renamed.

v2: Marek> removed gfx.flush in si_dma_copy_tile

Signed-off-by: Niels Ole Salscheider <niels_ole@salscheider-online.de>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>