doc: Update feature matrix

Since softpipe doesn't truely support multisample, I've not added softpipe
to the "Enhanced per-sample shading" even though with the advertised GLSL
level ARB_gpu_shader5 is advertised.

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
1 file changed