ARC: cleanup & modify _st32_huge_offset as it becomes widely used

As we start to use _st32_huge_offset in other places (i.e DSP code)
introduce optimized version with address shifted instruction which
doesn't produce extra instruction.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>