spl: fit: nand: skip bad block handling if NAND chip not fully defined

commit 9f6a14c4 ("spl: fit: nand: fix fit loading in case of bad blocks")
added support for adjusting the image offset to account for bad blocks.
However this requires nand_spl_adjust_offset() which requires fully defined
specifics of the NAND chip being used may not be avialable.

Allow skipping this support for drivers or configs which don't specify
the NAND chip details statically with defines.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Tom Rini <trini@konsulko.com>