verity: move userspace api to a new header file

We can now pull out the userspace API prototypes from the kernel header file.

BUG=chromium-os:19952
TEST=Ran unit tests from dm-verity.git.
     Ran platform_DMVerityCorruption and platform_DMVerityBitCorruption.
TESTED_ON=Alex

Change-Id: I2158f3519249c67bf652fdd1d9dfba4389928020
Reviewed-on: http://gerrit.chromium.org/gerrit/7104
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>
Tested-by: Mandeep Singh Baines <msb@chromium.org>
4 files changed