[LinuxBIOS] buildrom checkrom patch

[Myles Watson]

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