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 (closed)