softpipe: move some image filter parameters into a struct

softpipe: move some image filter parameters into a struct

This moves some of the image filter args into a struct,
and passes that instead, this is prep work for adding texture
gather support which needs new arguments.

review: make filter args const.

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