RISC-V: Include instruction hex in disassembly

RISC-V: Include instruction hex in disassembly

This was added to help debug issues using -d in_asm. It is
useful to see the instruction bytes, as one can detect if
one is trying to execute ASCII or device-tree magic.

Cc: Sagar Karandikar <sagark@eecs.berkeley.edu>
Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Signed-off-by: Michael Clark <mjc@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>