sb600spi.c: Generalise determin_generation() after Yangtze

Drop dead USE_YANGTZE_HEURISTICS code and add Promontory support.

Change-Id: I5aa7370025f5c1af56c6cb96194b6f3007d0ede7
Signed-off-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/36426
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
1 file changed