ARC: tweak _st32_huge_offset macro to have same behaviour with GNU & MWDT

Local variables in ASM macro works differently for GNU and MWDT
toolchains. In case of GNU toolchain they are local per each macro
instance, but in case of MWDT they are local per file where macro
is used.

To avoid issues when macro is used multiple times in one file let's
align _st32_huge_offset to have same behaviour with GNU & MWDT
toolchains.

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