arc: Rename ARCangel4 board to nSIM

arc: Rename ARCangel4 board to nSIM

ARCangel was one of the main development boards back in the day but
now it's gone and replaced by other boards like ARC SDP.

But we also used to have simulation platform very similar to ARCangel4
in terms of CPU settings as well as basic IO like UART. Even though
ARCangel4 is long gone now we have a replacement for simulation which is
a plain or stand-alone nSIM and Free nSIM.

Note Free nSIM is available for download here:
https://www.synopsys.com/cgi-bin/dwarcnsim/req1.cgi

And while at it:
 * Finally switch hex numerical values in nsim.h to defines from
   include/linux/sizes.h
 * Add defconfigs with ARC HS38 cores
 * Recreated all defconfigs with savedefconfig

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>