Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

Add the simplified ne2k_isa driver.  It is just a selective copy+paste
of the relevant parts from ns8390.c plus a little trivial hacking to
make it actually work.

It is true that the code is pretty ugly, but:
  a) ns8390.c is worse
  b) It is only 372 lines and no #ifdefs
  c) It works both in qemu/bochs and in real hardware
     and we all know it is easier to cleanup working code

Hope someone will find the time to rewrite this driver properly,
but until then at least for me this is an ok solution.

Signed-off-by: Pantelis Koukousoulas <pktoss@gmail.com>