ARC: nSIM: Make reorganization of board and SoC structure

Change source tree organization for Synopsys nSIM platform.
Classical ARC architectures arc_v2 arc_v3 moved to arc_classic
SoC and boards family.
nSIM SoCs were separated regarding series: EM, HS, SEM, VPX2.
This PR sould be seeing as the preparation for
addition new nSIM platform based on the RISC-V architecture.

Signed-off-by: Nikolay Agishev <agishev@synopsys.com>