ARC: gcc-m-cpu: use -mcpu=archs as a default for ARCv2 HS

Due to the fact that we use -mcpu=hs as a default for ARCv2 HS
the compiler doesn't generate multiply/divide/mac/64bit memory
operations instructions.

Fix that by using -mcpu=archs as a default for ARCv2 HS which is
fits for all existing boards with ARCv2 HS CPU.

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