Blackfin: bf52x/bf54x boards: drop unused nand page size

Now that the driver for the Blackfin on-chip NFC no longer uses/respects
the page_size from the platform resources (figures out the needs on the
fly), drop it from the platform resources.  This fixes some build errors
since the defines no longer exists.

Signed-off-by: Barry Song <barry.song@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>