BugLink: http://bugs.launchpad.net/bugs/1558553

The config option SYSTEM_EXTRA_CERTIFICATE reserves space in vmlinux file,
which is compressed to create the self-extracting bzImage. This patch adds the
capability of extracting the vmlinux, inserting the certificate, and
repackaging the result into a bzImage.

It only works if the resulting compressed vmlinux is smaller than the original.
Otherwise re-linking would be required. To make the reserved space allocate
actual space in bzImage, a null key is inserted into vmlinux before creating
the bzImage:

	make vmlinux
	scripts/insert-sys-cert -b vmlinux -c /dev/null
	make bzImage

After null key insertion, the script populates the rest of the reserved space
with random bytes, which have poor compression. After receiving a bzImage that
is created this way, actual certificate can be inserted into the bzImage:

	scripts/insert-sys-cert -s <System.map> -z <bzImage> -c <certfile>
Signed-off-by: Mehmet Kayaalp <mkayaalp@linux.vnet.ibm.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>