i965: Allow indirect GS input indexing in the scalar backend.

i965: Allow indirect GS input indexing in the scalar backend.

This allows arbitrary non-constant indices on GS input arrays,
both for the vertex index, and any array offsets beyond that.

All indirects are handled via the pull model.  We could potentially
handle indirect addressing of pushed data as well, but it would add
additional code complexity, and we usually have to pull inputs anyway
due to the sheer volume of input data.  Plus, marking pushed inputs
as live due to indirect addressing could exacerbate register pressure
problems pretty badly.  We'd need to be careful.

v2: Use updated MOV_INDIRECT opcode.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>