i965: add new VS_OPCODE_UNPACK_FLAGS_SIMD4X2

Splits the bottom 8 bits of f0.0 for further wrangling
in a SIMD4x2 program. The 4 bits corresponding to the channels in each
program flow are copied to the LSBs of dst.x visible to each flow.

This is useful for working with clipping flags in the VS.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
i965/Gen4-5: Set clip flags from clip distances

V2: Use the new VS_OPCODE_UNPACK_FLAGS_SIMD4X2 to correctly split the
flags for the two vertices being processed together.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
i965/clip: Track offset into the vertex for clipdistance

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
i956/clip: push dp4 into load_clip_distance

Soon the dp4 is only going to be used for fixed clip planes.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
i965/clip: Use clip distances for all user clipping

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
i965/clip: remove spurious clipvertex param

Nothing in the clipper uses gl_ClipVertex any more, so we don't care
where it is.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
i965/clip: Support clip distances for line clipping

This does the same thing as we do for triangle clipping -- select the
appropriate source (either dot(hpos,fixed plane) or a clipdistance
slot).

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
get rid of clip plane compaction