winsys/radeon: set/get the scanout flag with the tiling ioctls

winsys/radeon: set/get the scanout flag with the tiling ioctls

If we assume that all buffers allocated by the DDX are scanout, a new flag
that says "this is not scanout" has to be added to support the non-scanout
buffers and maintain backward compatibility.

This fixes bad rendering on Wayland.

The flag is defined as:
  #define RADEON_TILING_R600_NO_SCANOUT   RADEON_TILING_SWAP_16BIT

AFAIK, RADEON_TILING_SWAP_16BIT is not used on SI.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>