ARC: Add support for nSIM OSCI System C model

This adds support for an ARC Virtual Platform. This platform is based on the
System C standard promoted by the OSCI (Open System C Initiative) and uses
nSIM to simulate the ARC CPU core itself.

Users can build a virtual SoC by combining System C models of peripherals
and CPU cores.

Signed-off-by: Mischa Jonker <mjonker@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>