Add DejaGNU board file for Metaware+nSIM

New board definition (arc-sim-mdb) uses nSIM directly to run compiler tests,
instead of using GDB + nSIM_gdb combination. This board doesn't support GDB
as a test target. MetaWare is used as an interface to nSIM.

Signed-off-by: Anton Kolesov <anton.kolesov@synopsys.com>