target-i386: Add Intel SHA_NI instruction support.

Add SHA_NI feature bit. Its spec can be found at:
https://software.intel.com/sites/default/files/managed/39/c5/325462-sdm-vol-1-2abcd-3abcd.pdf



Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
Message-Id: <1481683803-10051-1-git-send-email-yi.y.sun@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>