This changes pfilter-builder.c so it really build in user space, but removing
register setting and creating output files instead.

Running this program creates 3 files, that correspond to the previous
three #ifdef conditions.  The files are:

      rules-plain.bin    this is used for the no-etherbone configuration
      rules-ebone.bin    etherbone setup
      rules-e+nic.bin    etherbon plus 7solution's wr-nic packet filter

The files begin with a magix 0x11223344 word, that allows the soft-core
to fix any endianness difference (so no hairy mishaps are expected when
switching to a different soft-core). Then the 40-bit command words are
saved as 64-bit vaules, LSB-first. The output file is thus an odd number
of words and no 64-bit alignment is required.

The first three instructions of the packet filter are used to compare
the destination mac address of the frame.  We now use a fake mac address,
and the LM32 code will change it while programming the binary.

Please look at this commit while ignoring white-space, as it changes
indentation while turning #ifdef/#else into if()/else .
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>