nv50/ir: rebase indirect temp arrays to 0, so that we use less lmem space

nv50/ir: rebase indirect temp arrays to 0, so that we use less lmem space

Reduces local memory usage in a lot of Metro 2033 Redux and a few KSP
shaders:

total local used in shared programs   : 54116 -> 30372 (-43.88%)

Probably modest advantage to execution, but it's an imporant
prerequisite to dropping some of the TGSI optimizations done by the
state tracker.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>