i965/nir: Make INTEL_DEBUG=ann work with NIR.

i965/nir: Make INTEL_DEBUG=ann work with NIR.

Now that we store a copy of the NIR shader, and don't immediately free
it, we can use it in annotations as well.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>