nv50: add comments about CB_AUX contents

Updates a few inconsistencies as well, like the size of the buffer,
location of the runout, etc.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
nv50: add support for textureFetch'ing MS textures

Creates two areas in the AUX constbuf:
 - Sample offsets for MS textures
 - Per-texture MS settings

When executing a textureFetch with a MS sampler, looks up that texture's
settings and adjusts the parameters given to the texfetch instruction.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
nv50: report glsl 1.50 now that gp tests pass

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
nv50: enable seamless cube maps/multisample textures for OpenGL 3.2

Some of the hardware support is missing. The NVIDIA-provided driver,
which claims 3.3 support fails a slew of the relevant tests as well.
This allows us to expose geometry shaders without doing the additional
work involved in supporting ARB_geometry_shader4.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>