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

This is a major rewrite of the legacy etherboot 3c90x driver using the
gPXE API for much improved performance over the legacy driver it
replaces.

This driver has been tested on 3c905, 3c905B, and 3c905C cards.

Reviewed-by: Stefan Hajnoczi <stefanha@gmail.com>
Reviewed-by: Marty Connor <mdc@etherboot.org>
Tested-by: Marty Connor <mdc@etherboot.org>
Tested-by: Daniel Verkamp <daniel@drv.nu>

Signed-off-by: Marty Connor <mdc@etherboot.org>