radv/ac: add support for TCS/TES inputs/outputs.

radv/ac: add support for TCS/TES inputs/outputs.

This adds support for the tessellation inputs/outputs to the
shader compiler, this is one of the main pieces of the patch.

It is very similiar to the radeonsi code (post merge we should
consider if there are better sharing opportunities). The main
differences from radeonsi, is that we can have "compact" varyings
for clip/cull/tess factors, and we have to add special handling
for these.

This consists of treating the const index from the deref different
depending on the compactness.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Signed-off-by: Dave Airlie <airlied@redhat.com>