docs: mark off nv50/nvc0 for ARB_sample_shading, update relnotes

relnotes weren't updated this whole time, so I went through all the
GL3.txt changes and picked out the nouveau ones since 10.1.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
2 files changed