softpipe: start adding gather support (v2)

This adds both ARB_texture_gather and the enhanced gather
for ARB_gpu_shader5.

This passes all the piglit tests, it relies on the GLSL
lowering pass to make textureGatherOffsets work.

v2: use inline to get gather component (Brian)
fix function name, add asserts (Brian)

Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
3 files changed