norflash: Add hack to hide start of NOR flash

This is a workaround for hiding U-Boot that is stored in the first 2
128k blocks, so we can put a BFS image into NOR to boot from (since
we do not have support for SD/MMC yet in Haiku).

When manually putting a BFS filesystem at block 3 we actually get
right up to the point where BootScript is attempted to be executed!