r600: Disable eight bit three channel formats

r600: Disable eight bit three channel formats

Commit 0899bf55 made some deqp-gles3 tests related to RGB8 PBOs fail
on R600 because it exposed PIPE_FORMAT_R8G8B8_UNORM and R600 doesn't
propely handle this. Disabling this format also for buffers fixes the
issue.

In addition, disabling also the related RGB8 integer formats for buffers
fixes some deqp-gles3 tests:

  dEQP-GLES3.functional.texture.specification.teximage2d_pbo.rgb8ui_cube
  dEQP-GLES3.functional.texture.specification.texsubimage2d_pbo.rgb8i_2d
  dEQP-GLES3.functional.texture.specification.texsubimage2d_pbo.rgb8i_cube
  dEQP-GLES3.functional.texture.specification.texsubimage2d_pbo.rgb8ui_2d
  dEQP-GLES3.functional.texture.specification.texsubimage2d_pbo.rgb8ui_cube
  dEQP-GLES3.functional.texture.specification.teximage3d_pbo.rgb8i_2d_array
  dEQP-GLES3.functional.texture.specification.teximage3d_pbo.rgb8i_3d
  dEQP-GLES3.functional.texture.specification.teximage3d_pbo.rgb8ui_2d_array
  dEQP-GLES3.functional.texture.specification.teximage3d_pbo.rgb8ui_3d
  dEQP-GLES3.functional.texture.specification.texsubimage3d_pbo.rgb8i_2d_array
  dEQP-GLES3.functional.texture.specification.texsubimage3d_pbo.rgb8i_3d
  dEQP-GLES3.functional.texture.specification.texsubimage3d_pbo.rgb8ui_2d_array
  dEQP-GLES3.functional.texture.specification.texsubimage3d_pbo.rgb8ui_3d

Fixes: 0899bf55
  st/mesa: Map MESA_FORMAT_RGB_UNORM8 <-> PIPE_FORMAT_R8G8B8_UNORM

Closes #2118

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Eric Anholt <eric@anholt.net>