etnaviv: use nir_lower_idiv(..) before opt loop
nir_lower_idiv(..) creates during its lowering isub instructions. Move nir_lower_idiv(..) before the opt loop to have a chance to optimize/lower isub away. Also drop the drop the halti dependency to make it easier to follow.
This fixes the following assert on GC3000: Unhandled ALU op: isub
Signed-off-by: Christian Gmeiner christian.gmeiner@gmail.com