Implement CRC32 algorithm for RISC-V.

Implement CRC32 algorithm for RISC-V.

Signed-off-by: Tim Newsome <tim@sifive.com>
Change-Id: Id437f78e74e3d837ff203f84c4eeb996bfad9a01
Reviewed-on: http://openocd.zylin.com/6076
Reviewed-by: Jan Matyas <matyas@codasip.com>
Reviewed-by: Marc Schink <dev@zapb.de>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins