gm107/ir: optimize 32-bit CONST load to mov

gm107/ir: optimize 32-bit CONST load to mov

This is not allowed for indirect accesses because the source
GPR might be erased by a subsequent instruction (WaR hazard)
if we don't emit a read dep bar.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>