CHROMIUM: config: enable DM_CRYPT target

CHROMIUM: config: enable DM_CRYPT target

The dm "crypt" target is needed for encrypted /var support. Additionally, since the
expected hash alg will be sha256, built it in, and ready future support for sha512
as a module.

BUG=chromium-os:22172
TEST=build, boot amd64-generic, verify target listed in "dmsetup targets"

Signed-off-by: Kees Cook <keescook@chromium.org>
Change-Id: I0f2396fdf613de9acf9d905177ffc00c5af6224c
Reviewed-on: https://gerrit.chromium.org/gerrit/15548
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Commit-Ready: Kees Cook <keescook@chromium.org>