cbfstool: improve specification of struct cbfs_file

Lock down its size and document some of the fields

Change-Id: I09fd6c80185345da0ae17d0f4498b50995fd1ec5
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: http://review.coreboot.org/10927
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
1 file changed