ARC: used 64bit MDB binary by default.

This significantly improve user experience as 32 bit mdb binary
require to install multiple libraries before it can be used on
modern linux distros.

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