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

We have EFI APIs for CPU I/O, PCI I/O, timers, console I/O, user
access and user memory allocation.

EFI executables are created using the vanilla GNU toolchain, with the
EXE header handcrafted in assembly and relocations generated by a
custom efilink utility.

reflect the fact that they allocate and deallocate user memory (i.e.
things reached through a userptr_t).