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

Signed-off-by: Michael Brown <mcb30@etherboot.org>

This brings us in to line with Linux definitions, and also simplifies
adding x86_64 support since both platforms have 2-byte shorts, 4-byte
ints and 8-byte long longs.

Drivers are not allowed to call printf().  Converted eprintf() to DBG(),
and removed spurious startup banner.

Fixed hardcoded inclusion of little_bswap.h

Use EIO rather than 1 as an error number.

Stripped out trailing whitespace to keep git happy.