linux: add support of Synopsys ARCHS38-based boards

This patch introduces support of new boards with ARC HS38 cores.

ARC HS38 is a new generation of ARC cores which utilize ARCv2 ISA.
As with ARC770 we're addind support for 2 boards for now:

 [1] Synopsys SDP board (AXS103)
     This is the same base-board as in AXS101 but with
     FPGA-based CPU-tile where ARCHs38 core is implemented.

 [2] nSIM
     Again this is the same simulation engine but configured for
     new instruction set and features of new CPU.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Felix Fietkau <nbd@openwrt.org>
Cc: Jo-Philipp Wich <jow@openwrt.org>
Cc: Jonas Gorski <jogo@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@48740 3c298f89-4303-0410-b956-a3cf2f4a3e73