sheep: migrate isa-l into sheepdog

isa-l is Intel Storage Acceleration Library which could accelerate
computing of erasure-code on intel CPU. We migrate the whole code
of isa-l v2.8
(https://01.org/sites/default/files/downloads/storage-acceleration-library/isa-l_open_src_2.8.tar.gz)
into sheepdog for following optimization of erasure-code.

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
sheep: modify Makefile to build isa-l into util

Add build script in util/Makefile to compose isa-l into sheepdog binary.

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
sheep: add funciton to compute ec by isa-l

Add new functions such as isa_decode_buffer().
It will choose correct funciton to compute ec when running.

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>