buildman: Switch ARC toolchain to the upstream version

buildman: Switch ARC toolchain to the upstream version

Back in the day we relied a lot on Synopsys own build of the GNU tools
for ARC processors, but since then we worked hard on getting all our changes
upstream and for a couple of years now we have ARCompact (AKA ARCv1)
and ARCv2 processors supported very well in upstream GCC, Binutils, GDB etc.

And so there's no need to use Synopsys forks any longer, thus we remove
all the references to that form and use upstream components as majority
of other architectures in U-Boot.

Thanks to Tom for pointing to that left-over!

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>