vboot: specify NEED_VB20_INTERNALS when needed

NEED_VB20_INTERNALS should always be specified when peeking
into vboot internal data structures.

BUG=b:124141368, chromium:956474
TEST=make clean && make test-abuild
BRANCH=none

Change-Id: I5a47a28350fd5a68efeff0d06ca150c1ae145412
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32452
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/security/vboot/bootmode.c

@@ -13,6 +13,8 @@
  * GNU General Public License for more details.
  */
 
+#define NEED_VB20_INTERNALS  /* Peeking into vb2_shared_data */
+
 #include <assert.h>
 #include <bootmode.h>
 #include <bootstate.h>