Unify ID_SECTION_OFFSET and mark it deprecated

We used to put the id section at -0x10, with some boards overriding
this to avoid collisions with romstraps.
Hardcode the location at -0x80, at the possible expense of some space
(0x70 bytes).
This also makes the section easier to find in a binary image.

At some point, CONFIG_ID_SECTION_OFFSET can be removed, so this option
is moved to src/Kconfig.deprecated_options.

Change-Id: I6ce2d6e94e57717939bda070bfe0c9df80ca2a89
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/549
Tested-by: build bot (Jenkins)
Reviewed-by: Peter Stuge <peter@stuge.se>