kernel flags: Add flags field to kernel preamble.

1. Increase kernel preamble revision from 2.1 to 2.2.
2. Add flags field to kernel preamble.
3. Update futility to accept flags parameter for vbutil_kernel and
cmd_sign for kernel.
4. Pass in an extra flags field to SignKernelBlob and
CreateKernelPreamble.

BUG=chrome-os-partner:35861
BRANCH=None
TEST=1) "make runalltests" completes successfully. 2) vboot_reference
compiles successfully for ryu. 3) Verified flags field in header using
futility show.

Change-Id: If9f06f98778a7339194c77090cbef4807d5e34e2
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://chromium-review.googlesource.com/245950
Tested-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Commit-Queue: Furquan Shaikh <furquan@chromium.org>
13 files changed