This is a trivial patch in terms of implementation.  It changes checkrom so that it doesn't depend on a magic number for ROM size, it just prints the size of the payload in Bytes and KBytes.

Another alternative is to make it configurable based on which payload you're using, but I'd rather it just print the message for the user.

Signed-off-by: Myles Watson <myles@pel.cs.byu.edu>