i965: Set shader name for generator from call site

i965: Set shader name for generator from call site

fs_generator no longer knows what stage it's generating code for, so
we have to set the debug name of the shader from the call site.

Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>