i965: Allow viewport array extensions with allow_higher_compat_version

i965: Allow viewport array extensions with allow_higher_compat_version

Also fix the obtuse comment.  I had to dig back through the commit logs
to find the real issue.  GL_ARB_viewport_array requires geometry
shaders, and in i965 the only way to have that is with a 3.2+ Core
profile context... or use allow_higher_compat_version.

This increases the maximum Compatibility profile version from 4.0 to 4.6
(on supported hardware) when the allow_higher_compat_version option is
used.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7118>