i965: Merge gen7_clip_state atom into gen6_clip_state atom.

i965: Merge gen7_clip_state atom into gen6_clip_state atom.

The original motivation was that gen6_clip_state ignored _NEW_POLYGON
as it didn't care about early culling.  The only other change was that
Gen6 ignored BRW_NEW_TES_PROG_DATA as it doesn't have tessellation
shaders, but listening to this is harmless as it'll never be signalled.

Now that we've added _NEW_POLYGON for is_drawing_lines/points, we can
merge the two as the distinction is meaningless.

This actually fixes a bug, though: Gen8+ was using the gen6_clip_state
atom because it doesn't care about early culling, but it also needs
BRW_NEW_TES_PROG_DATA, which was missing.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>