i965/fs: Add Gen < 6 runtime checks for line antialiasing.

i965/fs: Add Gen < 6 runtime checks for line antialiasing.

In Gen < 6 the hardware generates a runtime bit that indicates whether AA data
has to be sent as part of the framebuffer write SEND message. This affects the
specific case where we have setup antialiased line rendering and we render
polygons which have one face setup in GL_LINE mode (line antialiasing
will be used) and the other one in GL_FILL mode (no line antialiasing needed).

Currently we are not doing this runtime test and instead we always send AA
data, which produces incorrect rendering of the GL_FILL face of the polygon in
in the aforementioned scenario (verified in ironlake and gm45).

In Gen4 this is, likely, a regression introduced with commit 098acf6c843. In
Gen5 this has never worked properly. Gen > 5 are not affected by this.

The patch fixes the problem by adding the appropriate runtime check and
adjusting the framebuffer write message accordingly in the conflictive
scenario.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=78679

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>