We used to put the FCB in the first two NAND blocks and the DBBT
in the third and fourth block. It's much more space efficient to
put the FCB and DBBT together into the same eraseblock in different
pages. This way we can store four FCBs and four DBBTs instead of
two only.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>