vboot: convert secdata_kernel_crc to static function

Function is only used in 2secdata_kernel.c.  Convert to
a static function, and remove its header.

BUG=b:124141368, chromium:968464
TEST=make clean && make runtests
BRANCH=none

Signed-off-by: Joel Kitching <kitching@google.com>
Change-Id: Ib45abe68f0d4d025160c800c91dd2d2525dd1e3e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2641343
Tested-by: Joel Kitching <kitching@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@chromium.org>
2 files changed