Accept values of 2-5 for TopBottom, where the newly-added 4 and 5 values
mean a uniform layout. It does indicate WP layout but we don't handle that.

Also don't say "broken" when swapping erase regions in a top-boot chip.
That got retrospectively documented in the spec.
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>