LU-14880 libcfs: Use crypto/sha2.h if available

LU-14880 libcfs: Use crypto/sha2.h if available

As of Linux commit a24d22b225ce158651378869a6b88105c4bdb887
   crypto: sha - split sha.h into sha1.h and sha2.h

sha.h is removed and sha2.h or sha3.h is preferred.

Test-Parameters: trivial
Fixes: a813e81870 ("LU-12275 sec: add llcrypt as file encryption library")
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: Iead5e1cb23e79a400da3cbfeb4c35c834e821d62
Reviewed-on: https://review.whamcloud.com/44373
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>