* Make the makefs endian-ness configurable
* Allow the kernel suffix to be manually specified in the config
  file.

These are needed to use the little-endian MALTA build:

* we can't assume big-endian for the FS now!
* the big-endian and little-endian builds for MALTA use the same
  kernel file, so they end up installing into the same tftpboot
  file.  Ugh.
Add a new file for little-endian malta builds.
Allow X_KERNSUFFIX to override the filename of the kernel
going into /tftpboot
Make sure /tftpboot exists.