[MTD] [NOR] AT49BV6416 has swapped erase regions

The CFI information read from AT49BV6416 lists the erase regions in the
wrong order, causing problems when trying to erase or update the first
or last 64KiB block.

Work around this by inverting the "top boot" flag, which will
effectively reverse the order of the erase regions.

This chip is obsolete, but it's used in some existing designs.

Signed-off-by: Håvard Skinnemoen <haavard.skinnemoen@atmel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>