KEYS: Provide a script to extract the sys cert list from a vmlinux file

The supplied script takes a vmlinux file - and if necessary a System.map
file - locates the system certificates list and extracts it to the named
file.

Call as:

    ./scripts/extract-sys-certs vmlinux certs

if vmlinux contains symbols and:

    ./scripts/extract-sys-certs -s System.map vmlinux certs

if it does not.

It prints something like the following to stdout:

	Have 27 sections
	No symbols in vmlinux, trying System.map
	Have 80088 symbols
	Have 1346 bytes of certs at VMA 0xffffffff8201c540
	Certificate list in section .init.data
	Certificate list at file offset 0x141c540

If vmlinux contains symbols then that is used rather than System.map - even
if one is given.

Signed-off-by: David Howells <dhowells@redhat.com>