Add support to get layout from fmap (e.g. coreboot rom)

Using the --fmap argument one can give flashrom a layout in fmap
binary format like is found of coreboot roms (it will also look for
this on coreboot roms).

An example of how to use:
"flashrom -p programmer --fmap coreboot.rom -w coreboot.rom -i COREBOOT"
to only flash the COREBOOT fmap region.

The fmap functions are mostly copied from cbfstool.

Currently it is made mutually exclusive with --ifd while still
allowing --layout until we are more clever about this input.

Change-Id: I0e7fad38ed79a84d41358e1f175c36d255786c12
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
---
M Makefile
M cli_classic.c
M flashrom.8.tmpl
A fmap.c
A fmap.h
M layout.c
6 files changed, 251 insertions(+), 1 deletion(-)