Makefile: Explain process of handling CONFIG_* variables and cleanup.
Add an internal DMI decoder.

Previously we had to rely on dmidecode to decode the DMI/SMBIOS table.
This patch integrates a DMI decoder into flashrom. The old behavior of calling
dmidecode can be brought back by using CONFIG_INTERNAL_DMI=no.

Significant portions of this patch were taken from dmidecode, hence add its
authors to the copyright notice (dmidecode is also GPL2+). We do a few things
differently though. First of all we do more bounds checking to prevent accessing
unmapped memory. We do not support disovery via EFI (yet), but memory
scanning only. We handle the chassis-type lock bit correctly which dmidecode
did not for a long while.

The API to the rest of flashrom remains stable, but the output changes slightly.
To share as much code as possible (which actually is not much), i have added
dmi_fill methods that get called in dmi_init. They are reponsible to fill the
dmi_strings array and setting the is_laptop variable. After it is called, dmi_init
prints all dmi_strings. Previously the strings were printed in the order they were
discovered, followed by the chassis-type, which is now output earlier (in dmi_fill).

Because DJGPP does not support strnlen a simple implementation was added
for it.

This is still only available on x86; actually it is not even compiled in for other
architectures at all anymore.

Signed-off-by: Sean Nelson<audiohacked@gmail.com>
Signed-off-by: Stefan Tauner <stefan.tauner@student.tuwien.ac.at>
Tested-by: Maciej Pijanka <maciej.pijanka@gmail.com>
Tested-by: Idwer Vollering <vidwer@gmail.com>
Acked-by: Stefan Tauner <stefan.tauner@student.tuwien.ac.at>