[coreboot] [PATCH]remove pre-cbfs build system, pt. 3

[Patrick Georgi]

Hi,

this patch does away with CONFIG_ROM_PAYLOAD_START and
CONFIG_PAYLOAD_SIZE. Both were only really used in pre-cbfs, as the
payload's size isn't relevant for the build process anymore.

abuild is happily chugging along, but it isn't runtime tested. esp.
failover boards are affected by this, so if someone with a board
configured for failover could test this, and report back (basically: do
both fallback and normal still work?), I'd be grateful.

Various calculations in {no,}failovercalculation.lb are adapted
accordingly.

Signed-off-by: Patrick Georgi