doc: ARC: update ARC HW & tools support status

List of the changes:
 * add info about ARCv3 32bit HS5x which support has been
   upstreamed recently
 * mark HS6x MWDT toolchain support as Y

Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>