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

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.

Various specification documents disagree about the byte ordering of
UUIDs.  However, SMBIOS seems to use the standard in which everything is
in network-endian order.

This doesn't affect anything sent on the wire; only what gets printed on
the screen when the "uuid" variable is displayed.

implemented smbios_get_uuid().

set_fbms() will also update the E820 hidden region.

continually reallocating the real-mode stack.