ARC: Add support for ARC HS48 v3.1 processor

ARC: Add support for ARC HS48 v3.1 processor

This patch introduces a recently released significant update to ARC HS
family: ARC HS48.

One of the major ARC HS48 features is dual-issue pipeline which requires a
little bit modified instruction scheduling compared to single-issue cores
(HS38), thus new "-mcpu/--with-cpu=hs4x".

Also to address some peculiarities of early designs based on HS48 we
introduced yet another "-mcpu/--with-cpu=hs4x_rel31" which we're going to use
as well on some of our development boards.

Signed-off-by: Evgeniy Didin <didin@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: arc-buildroot@synopsys.com
[Peter: fixup check-package warnings]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>