vboot2: use common header size fields

Add functions for verifying object integrity using common header size
fields.  Convert vb2_packed_key2 to use the the new functions.  This
isn't much prettier for packed keys; the benefit is more obvious for
keyblocks (coming next).

BUG=chromium:423882
BRANCH=none
TEST=VBOOT2=1 make runtests

Change-Id: I0c09533368abb7ced3b5ac622a15e62832413b7f
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/226874
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
diff --git a/Makefile b/Makefile
index c72c6a7..146c042 100644
--- a/Makefile
+++ b/Makefile
@@ -283,6 +283,7 @@
 FWLIB2_SRCS = \
 	firmware/2lib/2api.c \
 	firmware/2lib/2common.c \
+	firmware/2lib/2common2.c \
 	firmware/2lib/2crc8.c \
 	firmware/2lib/2misc.c \
 	firmware/2lib/2nvstorage.c \