nouveau/compiler: Allow to omit line numbers when printing instructions

nouveau/compiler: Allow to omit line numbers when printing instructions

This comes in handy when checking "NV50_PROG_DEBUG=1" outputs with diff!

V2:
 - Use environmental variable (Karol Herbst)
V3:
 - Use the already populated nv50_ir_prog_info to forward information to the
   print pass (Pierre Moreau)
V4:
 - get rid of default value in PrintPass constructor

Signed-off-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Reviewed-by: Pierre Moreau <pierre.morrow@free.fr>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>