MIPS r6 encodes jr as jalr zero, and jr.hb as jalr.hb zero, so add these
encodings to the MIPS disassembly table.

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>
Message-Id: <1443788657-14537-3-git-send-email-james.hogan@imgtec.com>