Makefile: Add filelist to help

The filelist target has been around for a while, but was never added
to the help.  Add it now.

Change-Id: Idc24ecc8028fc61c6b798c0c81431b05dfa25b0e
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/23472
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
1 file changed