nv50/ir: only use FILE_LOCAL_MEMORY for temp arrays that use indirection

nv50/ir: only use FILE_LOCAL_MEMORY for temp arrays that use indirection

Previously we were treating any indirect temp array usage to mean that
everything should end up in lmem. The MemoryOpt pass would clean a lot
of that up later, but in the meanwhile we would lose a lot of
opportunity for optimization.

This helps a lot of Metro 2033 Redux and a handful of KSP shaders:

total instructions in shared programs : 6288373 -> 6261517 (-0.43%)
total gprs used in shared programs    : 944051 -> 945131 (0.11%)
total local used in shared programs   : 54116 -> 54116 (0.00%)

A typical case is for register usage to double and for instructions to
halve. A future commit can also optimize local memory usage size to be
reduced with better packing.

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