verity: implement alloc_page and __free_page

These are needed by a future (next CL) change to dm-bht.c.

BUG=chromium-os:9752
TEST=Ran dm-verity.git unit tests.

Change-Id: I4d7ad73dc62d6d72959d1b1429e3c64714b08d09
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Reviewed-on: http://gerrit.chromium.org/gerrit/6783
Reviewed-by: Will Drewry <wad@chromium.org>
1 file changed